NAS DrivesUpdated
Updated

CMR vs SMR for NAS

Why CMR is the safe choice for RAID, with live UK prices

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Quick answer

Use CMR drives in a NAS, not SMR. CMR handles random writes and RAID rebuilds at a steady speed, while SMR slows dramatically under sustained writes and can take so long to rebuild that the array drops the drive and the rebuild fails. SMR is fine for cold archival or single-drive backup, but for any RAID NAS, CMR drives like IronWolf, WD Red Plus, Red Pro, Exos or Toshiba N300 are the right choice.

As of 8 July 2026
Best price per TB
£9.04
Products tracked
166
Prices updated
5 hours ago

CMR vs SMR at a glance

CMRSMR
How tracks are writtenNon-overlapping, written independentlyOverlapping like roof shingles
Sustained write speedSteady and predictableDrops sharply once cache fills
RAID rebuild behaviourRebuilds at normal speedVery slow, can time out and drop the drive
Suitable for RAID NASYesNo, avoid
Good forNAS, RAID, busy multi-user workloadsCold archive, single-drive backup, light use
Typical NAS examplesIronWolf, WD Red Plus, Red Pro, Exos, N300Older WD Red EFAX 2 to 6TB, Barracuda, many desktop drives

Why SMR struggles in a NAS

SMR, shingled magnetic recording, packs more data onto a platter by overlapping write tracks like roof tiles. That raises capacity per pound, but it has a catch: to change data in one track the drive often has to rewrite neighbouring tracks too. Drives hide this with a small cache region and reshuffle data in the background, which works fine for light, bursty use. Under sustained writing, the cache fills and write speed falls off a cliff, sometimes to a fraction of what the drive managed at the start.

In a RAID NAS that behaviour is dangerous. When a drive fails and you fit a replacement, the array rebuilds by writing a continuous stream of data to the new drive. That is exactly the sustained-write workload SMR handles worst. The rebuild can crawl for days, and crucially it can take so long that the RAID controller decides the drive is unresponsive and drops it from the array. At that point the rebuild fails, and if a second drive then fails you can lose the lot. CMR rebuilds at a steady, predictable pace and avoids this trap.

How to spot and avoid SMR

The infamous example is plain WD Red in the 2 to 6TB range, the EFAX model numbers, which quietly used SMR and caused real-world rebuild failures before the technology was disclosed. WD Red Plus is the CMR replacement and is the drive you actually want. Seagate Barracuda and many cheap desktop or external drives are also SMR. Manufacturers do not always print SMR or CMR on the box, so check the specific model number against the manufacturer's published list, or use a community CMR/SMR reference, before you buy.

Proper NAS drives are CMR by design. Seagate IronWolf and IronWolf Pro, WD Red Plus and Red Pro, Seagate Exos and Toshiba N300 are all CMR and safe for RAID. The headline workload ratings tell the same story: 180 TB/year for IronWolf, WD Red Plus and N300, and 300 TB/year for IronWolf Pro, Red Pro and Exos. SMR is not evil, it is just the wrong tool here. Keep it for a cold archive disk or a single-drive backup target where you write occasionally and read often, and keep it out of any RAID array.

Which recording type for your job

Use CMR if

  • The drive goes into a RAID array of any kind
  • You expect sustained writes, backups or busy multi-user access
  • You ever need a fast, reliable rebuild after a failure
  • It is the main storage in a NAS that matters to you

SMR is acceptable only if

  • It is a single drive, not part of a RAID array
  • The workload is mostly reads with occasional writes
  • It is a cold archive or an offline backup disk
  • You have verified it will never be asked to rebuild an array

CMR NAS drives, by price per TB

Price per
166 products
ProductCapacityPrice£ / TBTypePrime
Seagate Exos X16, 6TB, Enterprise Internal Hard Drive, SAS, 3.5", for Business and Data Centre (ST6000NM0095)Used16.6 TB£150.00£9.04Enterprise HDD · SASCMREnterprise-
Western Digital Ultrastar DC HC520 (HUH721212AL5204) SAS Enterprise HDD 7200 RPM, 12 TBUsed12 TB£225.00£18.75Enterprise HDD · SASCMREnterprise-
Seagate Exos 28TB internal server hard drive ST28000NM000C 3.5" HDD SATA 6Gb/s 7200RPM 512MB Cache (Renewed)Renewed28 TB£591.14£21.11Enterprise HDD · SATACMREnterprisePrime
Seagate Exos 26TB Internal Hard Drive, 3.5 Inch HDD, SATA3, 256MB Cache (Renewed)Renewed26 TB£594.99£22.88Enterprise HDD · SATACMREnterprise-
Seagate EXOS X24 24TB Interne Festplatte 3.5 Zoll SATA 3 Gbit/s 512 MB, ST24000NM000C (Renewed)Renewed24 TB£551.57£22.98Enterprise HDD · SATACMREnterprisePrime
WD Red Pro 12TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB CacheUsed12 TB£279.95£23.33NAS HDD · SATACMR-
WD Ultrastar DC HC530 14TB 7200RPM SATA 6Gb/s 3.5" Enterprise HDD - WUH721414ALE6L4 (Renewed)Renewed14 TB£330.40£23.60Enterprise HDD · SATACMREnterprisePrime
Seagate EXOS X16 16TB Interne Festplatte 3.5 Zoll SATA 6 Gbit/s 256 MB, ST16000NM001G (Renewed)Renewed16 TB£383.18£23.95Enterprise HDD · SATACMREnterprisePrime
HGST WD Ultrastar DC HC510 10TB 7200RPM SATA 6Gb/s 3.5" SED Hard Drive - HUH721010ALE601 (0F27605) (Renewed)Renewed10 TB£241.99£24.20Enterprise HDD · SATACMREnterprisePrime
Seagate IronWolf, 8 TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 5,400 RPM, 256MB Cache, for RAID Network Attached Storage, 3 year Rescue Services (ST8000VN004)Used8 TB£200.00£25.00NAS HDD · SATACMR-
Seagate IronWolf 8TB NAS Hard Drive 3.5" 5400RPM 256MB CacheUsed8 TB£200.00£25.00NAS HDD · SATACMR-
Seagate IronWolf Pro 20TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Rescue Services - Frustration Free Packaging (ST20000NTZ01)Used20 TB£520.20£26.01NAS HDD · SATACMR-
Western Digital Ultrastar DC HC550 Enterprise-Festplatte 18 TB (3,5 inch, SATA 6 GB/s, SAS 12 GB/s, 7200 U/min, 512 MB Cache) (Renewed)Renewed18 TB£490.00£27.22Enterprise HDD · SASCMREnterprise-
WD Red Plus 8TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, CMR, 128MB Cache, 3 Year WarrantyUsed8 TB£219.99£27.50NAS HDD · SATACMR-
WD Red Plus 8TB NAS 3.5" Internal Hard Drive - 5640 RPM Class, SATA 6 Gb/s, CMR, 128MB CacheUsed8 TB£219.99£27.50NAS HDD · SATACMR-
Seagate Exos X16 14TB server internal hard drive ST14000NM001G 3.5" HDD SATA 6Gb/s 7200RPM 256MB Cache14 TB£384.96£27.50Enterprise HDD · SATACMREnterprisePrime
Seagate Skyhawk 4TB, Video Internal Hard Drive, 3.5", SATA, 6Gb/s, 64MB Cache, for DVR/NVR Security Camera System, with Drive Health Management, Data Rescue Services, FFP (ST4000VXZ16)Used4 TB£111.91£27.98NAS HDD · SATACMRPrime
Western Digital Ultrastar DC HC530 (WUH721414ALE6L4) SATA Enterprise HDD 7200 RPM, 14 TB14 TB£395.00£28.21Enterprise HDD · SATACMREnterprise-
Seagate Exos X18 Enterprise Class, 18TB, Enterprise Internal Hard Drive, SATA, 3,5" 6Gbit/s, 128MB cache ((ST18000NM000J)Used18 TB£510.99£28.39Enterprise HDD · SATACMREnterprise-
Seagate EXOS X18 18TB ST18000NM000J Interne Server Festplatte, 3,5 Zoll HDD SATA 6GB/S 7200RPM 256MB 24X7 Verfügbarkeit (Renewed)Renewed18 TB£511.77£28.43Enterprise HDD · SATACMREnterprisePrime
Western Digital Ultrastar DC HC550 Enterprise Hard Drive 18TB (3.5" SATA 6Gbps, SAS 12Gbps, 7200RPM, 512MB Cache)18 TB£525.00£29.17Enterprise HDD · SASCMREnterprise-
Western Digital Ultrastar DC HC550 3.5" 16000 GB Serial ATA III16 TB£470.00£29.38Enterprise HDD · SATACMREnterprise-
WD Ultrastar DC 0F38462 16TB 3.5" Enterprise SATA HDD/Hard Drive 7200rpm16 TB£475.00£29.69Enterprise HDD · SATACMREnterprise-
WD Red Pro 24TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB CacheUsed24 TB£716.68£29.86NAS HDD · SATACMRPrime
Seagate IronWolf Pro 14 TB NAS RAID Internal Hard Drive - 7,200 RPM SATA 6 Gb/s 3.5-inch (ST14000NE0008)14 TB£420.00£30.00NAS HDD · SATACMR-
WD Red Pro 20TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB CacheUsed20 TB£601.76£30.09NAS HDD · SATACMRPrime
Seagate IronWolf Pro, NAS Internal Hard Drive 20TB HDD, 3.5 Inch, 7200 rpm, CMR, 256 MB Cache, SATA 6GB/S, Silver, Model No.: ST20000NE00020 TB£610.77£30.54NAS HDD · SATACMRPrime
Seagate Exos X18 Enterprise Class, 18TB, Enterprise Internal Hard Drive, SATA, 3,5" 6Gbit/s, 128MB cache ((ST18000NM000J)18 TB£550.00£30.56Enterprise HDD · SATACMREnterprise-
Seagate IronWolf Pro, 14 TB, Enterprise NAS Internal HDD –CMR 3.5 Inch, SATA 6 Gb/s, 7,200 RPM, 256 MB Cache for RAID Network Attached Storage, 3 year Rescue Services (ST14000NT001)14 TB£435.00£31.07Enterprise HDD · SATACMREnterprise-
Seagate IronWolf PRO 18TB Interne Festplatte CMR 3.5 Zoll SATA III 256 MB, ST18000NE000 (Renewed)Renewed18 TB£560.00£31.11NAS HDD · SATACMR-
Seagate IronWolf Pro 18TB NAS HDD, ST18000NE000 SATA 6Gb/s 3.5" (Renewed)Renewed18 TB£560.00£31.11NAS HDD · SATACMR-
Seagate IronWolf Pro 16TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST16000NTZ01)Used16 TB£500.00£31.25NAS HDD · SATACMR-
Seagate IronWolf Pro 6TB Interne hard disc 8.9cm (3.5 Zoll) SATA III ST6000NE000 BulkUsed6 TB£189.00£31.50NAS HDD · SATACMR-
Western Digital Ultrastar DC HC310 (HUS726T6TALE6L4) SATA Enterprise HDD 7200 RPM, 6 TBUsed6 TB£189.23£31.54Enterprise HDD · SATACMREnterprise-
WD 10TB WUS721010ALE6L4 Ultrastar DC HC330* Ent.10 TB£317.90£31.79Enterprise HDD · SATACMREnterprise-
Seagate IronWolf Pro 16TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST16000NTZ01)16 TB£514.99£32.19NAS HDD · SATACMRPrime
Seagate SkyHawk 6TB, Video Internal Hard Drive, 3.5", SATA, 6Gb/s, 64MB Cache, for DVR/NVR Security Camera System, with Drive Health Management, Data Rescue Services, FFP (ST6000VXZ09)6 TB£198.20£33.03NAS HDD · SATACMRPrime
Seagate 6TB IronWolf ST6000VN001 5400RPM 256MB NASUsed6 TB£199.00£33.17NAS HDD · SATACMR-
Seagate IronWolf 8TB, Internal NAS HDD, CMR, 3.5 Inch, SATA, 6GB/s, 5.400 RPM, 256MB Cache, Data Rescue Services, (ST8000VNZ02)Used8 TB£265.99£33.25NAS HDD · SATACMR-
WD Red Pro 14TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR Recording Technology, 512MB Cache14 TB£465.95£33.28NAS HDD · SATACMR-
WD Red 6TB NAS 3.5 Inch Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, CMR, 64 MB Cache - WD60EFRX Red WD60EFRXUsed6 TB£199.99£33.33NAS HDD · SATACMR-
Toshiba 16TB N300 NAS Internal HDD - 3.5" SATA-3 512MB Cache 6GB/s 7200RPM Internal Hard Drive 7/24 NAS Unit Server & Security Drive (HDWG51GUZSVA)16 TB£539.88£33.74NAS HDD · SATACMR-
Seagate SkyHawk 8TB, Video Internal Hard HDD, 3.5", SATA 6Gb/s, 256MB Cache, for DVR NVR Security Camera System, with in-house Data Rescue Services, FFP (ST8000VXZ10)8 TB£273.22£34.15NAS HDD · SATACMRPrime
Seagate IronWolf Pro 20TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Rescue Services - Frustration Free Packaging (ST20000NTZ01)20 TB£689.99£34.50NAS HDD · SATACMRPrime
Seagate IronWolf 4TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 5.400 RPM, 256MB Cache, for RAID Network Attached Storage, Data Rescue Services (ST4000VNZ06)Used4 TB£138.97£34.74NAS HDD · SATACMRPrime
G-DRIVE 26TB Enterprise Class Desktop external Hard Drive, HDD up to 260 MB/s, USB-C, USB 3.2 Gen 2 (10Gbps), 7200RPM Ultrastar, Fast backup, Premium, Industrial enclosure26 TB£914.71£35.18Enterprise HDD · SATACMREnterprisePrime
Seagate IronWolf Pro 12TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST12000NTZ01)12 TB£423.00£35.25NAS HDD · SATACMR-
Seagate Skyhawk 4TB, Video Internal Hard Drive, 3.5", SATA, 6Gb/s, 64MB Cache, for DVR/NVR Security Camera System, with Drive Health Management, Data Rescue Services, FFP (ST4000VXZ16)4 TB£141.50£35.38NAS HDD · SATACMRPrime
Seagate IronWolf Pro 3.5-inch 18TB Internal Hard Disk HDD CMR 3.5 Inch Data Recovery ST18000NT001 6Gb/s 256MB 7200 rpm 24 Hour Operation PC18 TB£637.10£35.39NAS HDD · SATACMR-
Seagate IronWolf Pro, 12 TB, NAS Internal Hard Drive, CMR 3.5 Inch, SATA 6 Gb/s 7,200 RPM, 256 MB Cache, for RAID Network Attached Storage, 3 years Rescue Services, FFP (ST12000NE0008)12 TB£425.00£35.42NAS HDD · SATACMR-
Toshiba 12TB N300 Internal Hard Drive – NAS 3.5 Inch SATA HDD Supports Up to 8 Drive Bays Designed for 24/7 NAS Systems, New Generation (HDWG21CUZSVA)12 TB£434.97£36.25NAS HDD · SATACMR-
WESTERN DIGITAL ULTRASTAR DC HC310 HUS726T6TAL5204 3.5" 6000 GB SAS Black6 TB£218.90£36.48Enterprise HDD · SASCMREnterprise-
Seagate IronWolf Pro 30TB, NAS internal hard drive, 3.5", 7200 U/Min, CMR, 512 MB Cache, SATA 6 GB/S, Data Rescue Service (ST30000NTZ11)30 TB£1,095.99£36.53NAS HDD · SATACMRPrime
Seagate IronWolf Pro 24TB, NAS Internal Hard Drive, 3.5 Inch, 7.200 U/Min, CMR, 256MB Cache, SATA 6 GB/S, incl. Datat Rescue Service (ST24000NTZ02)24 TB£878.99£36.62NAS HDD · SATACMRPrime
Seagate IronWolf, 16 TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 5,400 RPM, 256MB Cache, for RAID Network Attached Storage, 3 year Rescue Services (ST16000VN001)16 TB£590.00£36.88NAS HDD · SATACMR-
Seagate IronWolf 6TB NAS 3.5" SATA HDD/Hard Drive6 TB£223.00£37.17NAS HDD · SATACMR-
Seagate Skyhawk AI 16TB, Video Internal Hard Drive, 3.5 Inch, SATA, 6Gb/s, 256MB Cache, for DVR/NVR Security Camera System, Data Rescue Service (ST16000VE004)16 TB£595.00£37.19NAS HDD · SATACMR-
WD Purple Pro 24TB Smart Video 3.5" Internal Hard Drive, AllFrame AI Technology, 7200 RPM, SATA 6 GB/s, 550TB/yr, 512MB Cache24 TB£897.00£37.38NAS HDD · SATACMR-
Seagate IronWolf Pro 8TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST8000NTZ01)8 TB£299.20£37.40NAS HDD · SATACMRPrime
Seagate IronWolf Pro, 4 TB, NAS Internal Hard Drive, CMR 3.5 Inch, SATA 6 Gb/s 7,200 RPM, 256 MB Cache, for RAID Network Attached Storage, 3 years Rescue Services, FFP (ST4000NE001)Used4 TB£150.00£37.50NAS HDD · SATACMR-
WD Red Pro 26TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB Cache26 TB£981.58£37.75NAS HDD · SATACMR-
WD Ultrastar DC HC555 Hard Drive Data Centre 12 TB Internal 3.5 Inches (8.9 cm)12 TB£455.90£37.99Enterprise HDD · SATACMREnterprise-
Seagate IronWolf, 8 TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 5,400 RPM, 256MB Cache, for RAID Network Attached Storage, 3 year Rescue Services (ST8000VN004)8 TB£303.98£38.00NAS HDD · SATACMR-
Seagate IronWolf Pro ST8000NE001 8TB Internal 3.5" Inch SATA 6Gb/s 7200rpm Server HDD (Renewed)Renewed8 TB£303.99£38.00NAS HDD · SATACMR-
Seagate IronWolf 2TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 5900 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST2000VNZ03)Used2 TB£76.10£38.05NAS HDD · SATACMRPrime
Western Digital Hitachi HDD Int 10TB Ultrastar 72 SATA 3.5 HUH721010ALE60410 TB£382.38£38.24Enterprise HDD · SATACMREnterprise-
Seagate IronWolf 8TB, Internal NAS HDD, CMR, 3.5 Inch, SATA, 6GB/s, 5.400 RPM, 256MB Cache, Data Rescue Services, (ST8000VNZ02)8 TB£310.00£38.75NAS HDD · SATACMR-
Seagate Exos 7E10 4TB Internal Hard Drive HDD - 3.5 Inch 512e/4Kn SAS 6GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST4000NM000B)Used4 TB£155.22£38.81Enterprise HDD · SASCMREnterprise-
WD Red Plus 10TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6Gb/s, CMR, 256MB Cache10 TB£395.29£39.53NAS HDD · SATACMR-
Seagate IronWolf, 8 TB, Enterprise Internal NAS HDD – CMR 3.5 Inch, SATA 6 Gb/s, 7,200 RPM, 256 MB Cache for RAID NAS, Rescue Services (ST8000NT002)8 TB£319.00£39.88NAS HDD · SATACMR-
TOSHIBA N300 12TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 Gb/s 7200 RPM 512 MB Cache - HDWG51CXZSTA12 TB£478.77£39.90NAS HDD · SATACMR-
Toshiba N300 12TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 Gb/s 7200 RPM 256 MB Cache - HDWG21CXZSTA12 TB£478.77£39.90NAS HDD · SATACMR-
Seagate 10 TB IronWolf NAS 3.5 Inch Hard Drive ST10000VN0008 (SATA 6 Gb/s/256 MB/7200 RPM)10 TB£400.00£40.00NAS HDD · SATACMR-
WD Red Pro 18TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 512MB Cache18 TB£729.98£40.55NAS HDD · SATACMR-
Toshiba N300 8TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 GB/s 7200 RPM 256 MB Cache - HDWG180XZSTA8 TB£325.00£40.63NAS HDD · SATACMR-
Seagate IronWolf 4TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 5.400 RPM, 256MB Cache, for RAID Network Attached Storage, Data Rescue Services (ST4000VNZ06)4 TB£165.00£41.25NAS HDD · SATACMRPrime
Seagate IronWolf, 6 TB internal Hard Drive, NAS HDD, 3.5 Inch, 5400 U/Min, CMR, 64 MB Cache, SATA 6 GB/s, 3 Years Rescue Service, Modellnr.: ST6000VN0066 TB£249.95£41.66NAS HDD · SATACMR-
WD Red Plus 10TB NAS Hard Disk Drive - 5400 RPM Class SATA 6Gb/s, CMR, 256MB Cache, 3.5 Inch10 TB£420.00£42.00NAS HDD · SATACMR-
WD Purple 4TB Surveillance 3.5" Internal Hard Drive, AllFrame Technology, 180BT/yr, 256MB Cache, 3 Year WarrantyUsed4 TB£169.00£42.25NAS HDD · SATACMR-
WD Red Plus 4TB NAS 3.5" Internal Hard Drive - 5400 RPM, SATA 6Gb/s, CMR, 128MB CacheUsed4 TB£169.65£42.41NAS HDD · SATACMR-
Western Digital WD Red Plus Internal Hard Drive 8TB CMR 3.5 inch SATA 5640 rpm 256MB NAS WD80EFPX-AJP Eco Package8 TB£339.88£42.49NAS HDD · SATACMR-
Seagate IronWolf 4 TB NAS Internal Hard Drive HDD – CMR 3.5 Inch SATA 6 Gb/s 5,400 RPM 256 MB Cache for RAID Network Attached Storage, Rescue Services (ST4000VN006)4 TB£169.98£42.50NAS HDD · SATACMR-
Seagate IronWolf Pro 4TB, Enterprise Internal NAS HDD, CMR, 3.5 Inch, SATA 6GB/s, 7.200 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST4000NTZ01)4 TB£169.99£42.50NAS HDD · SATACMRPrime
Seagate Exos 7E10 8TB Internal Hard Drive HDD - 3.5 Inch 512e/4Kn SAS 6GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST8000NM017B)8 TB£339.99£42.50Enterprise HDD · SASCMREnterprise-
Seagate IronWolf, 4 TB, NAS, Internal Hard Drive, CMR 3.5 Inch, SATA, 6GB/s, 5,900 RPM, 64MB Cache, for RAID Network Attached Storage, 3 year Rescue Services (ST4000VN008)4 TB£170.99£42.75NAS HDD · SATACMR-
Synology DS423 40TB 4 Bay Desktop NAS Solution installed with 4 x 10TB Seagate Ironwolf Drives40 TB£1,729.88£43.25NAS HDD · SATACMR-
Synology DS423 40TB 4 Bay Desktop NAS Solution installed with 4 x 10TB Western Digital Red Plus Drives40 TB£1,733.00£43.33NAS HDD · SATACMR-
TOSHIBA N300 8TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 GB/s 7200 RPM 512 MB Cache - HDWG780XZSTA8 TB£347.99£43.50NAS HDD · SATACMR-
WD Red Pro 12TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB Cache12 TB£522.04£43.50NAS HDD · SATACMR-
WD Red Pro 8TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache8 TB£348.97£43.62NAS HDD · SATACMR-
Seagate IronWolf Pro ST8000NE001 8TB Internal 3.5" SATA 6Gb/s 7200rpm - 256MB - With 2 Years Rescue Data Recovery Service Plan8 TB£349.00£43.63NAS HDD · SATACMR-
Seagate IronWolf 6TB, Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 5400 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST6000VNZ06)6 TB£262.31£43.72NAS HDD · SATACMRPrime
Seagate IronWolf 10TB, NAS, Internal Hard Drive, CMR, 3.5 Inch, SATA, 6GB/s, 7.200 RPM, 256MB Cache, for RAID Network Attached Storage, Data Rescue Services, FFP (ST10000VNZ00)10 TB£438.99£43.90NAS HDD · SATACMR-
Seagate IronWolf Pro, 4 TB, NAS Internal Hard Drive, CMR 3.5 Inch, SATA 6 Gb/s 7,200 RPM, 256 MB Cache, for RAID Network Attached Storage, 3 years Rescue Services, FFP (ST4000NE001)4 TB£175.99£44.00NAS HDD · SATACMR-
Toshiba N300 8TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 GB/s 7200 RPM 256 MB Cache - HDWG480XZSTA, Silver8 TB£355.00£44.38NAS HDD · SATACMR-
Seagate Exos 7E10 10TB Internal Hard Drive HDD - 3.5 Inch 4Kn SAS 6GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST10000NM002B)10 TB£447.99£44.80Enterprise HDD · SASCMREnterprise-
WD Red Plus 8TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, CMR, 128MB Cache, 3 Year Warranty8 TB£359.99£45.00NAS HDD · SATACMR-
WD Red Pro 12 TB 3.5 Inch NAS Internal Hard Drive - 7200 RPM - WD121KFBX12 TB£543.87£45.32NAS HDD · SATACMR-
WD Purple 4TB Surveillance 3.5" Internal Hard Drive, AllFrame Technology, 180BT/yr, 256MB Cache, 3 Year Warranty4 TB£182.51£45.63NAS HDD · SATACMR-
WD Red Plus 6TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6Gb/s, CMR, 256MB Cache6 TB£274.55£45.76NAS HDD · SATACMRPrime
TOSHIBA N300 6TB NAS 3.5-Inch Internal Hard Drive - CMR SATA 6 GB/s 7200 RPM 512 MB Cache - HDWG760XZSTA6 TB£275.75£45.96NAS HDD · SATACMR-
TOSHIBA 8.9cm (3.5") 8TB SATA3 NAS N300 7200RPM internal bulk8 TB£370.00£46.25NAS HDD · SATACMR-
Toshiba MG09ACA16TE / JP-EC 7,200 rpm SATA 24x7 RV Sensor, Helium-Filled Hard Drive16 TB£742.95£46.43Enterprise HDD · SATACMREnterprisePrime
Toshiba 6TB N300 Internal Hard Drive – NAS 3.5 Inch SATA HDD Supports Up to 8 Drive Bays Designed for 24/7 NAS Systems, New Generation (HDWG460UZSVA)6 TB£278.75£46.46NAS HDD · SATACMR-
WD Red Pro 20TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR Recording Technology, 512MB Cache20 TB£929.99£46.50NAS HDD · SATACMR-
WD Red Plus 2TB NAS 3.5" Internal Hard Drive - 5400 RPM, SATA 6 Gb/s, CMR, 64MB CacheUsed2 TB£93.16£46.58NAS HDD · SATACMRPrime
WD Red Pro 20TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB Cache20 TB£937.13£46.86NAS HDD · SATACMR-
Seagate IronWolf Pro 32TB, NAS internal hard drive, 3.5", 7200 U/Min, CMR, 512 MB Cache, SATA 6 GB/S, Data Rescue Service (ST32000NT00)32 TB£1,499.99£46.87NAS HDD · SATACMR-
Seagate IronWolf Pro, 10TB, Internal Hard Drive, NAS, 3.5 Inch, SATA, 6GB/s, 7200 RPM, 256MB Cache, for RAID Network Attached Storage, 3 year Rescue Services, FFP (ST10000NEZ008)10 TB£469.99£47.00NAS HDD · SATACMR-
WD Red Plus 4TB NAS 3.5" Internal Hard Drive - 5400 RPM, SATA 6Gb/s, CMR, 128MB Cache4 TB£188.50£47.13NAS HDD · SATACMR-
Seagate Exos 7E8, 6TB, Enterprise Internal Hard Drive, SATA, 3.5", for Business and Data Centre (ST6000NM0115)8.6 TB£406.00£47.21Enterprise HDD · SATACMREnterprise-
Seagate IronWolf Pro 12 TB Internal Hard Drive 7200 RPM for NAS - ST12000NT00112 TB£567.00£47.25NAS HDD · SATACMR-
WD Red Pro 8TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache8 TB£379.99£47.50NAS HDD · SATACMR-
WD Red Pro 24TB NAS 3.5" Internal Hard Drive - 7200 RPM, SATA 6 Gb/s, CMR, 512MB Cache24 TB£1,141.78£47.57NAS HDD · SATACMR-
Synology DS423 32TB 4 Bay Desktop NAS Solution installed with 4 x 8TB Western Digital Red Plus Drives32 TB£1,580.00£49.38NAS HDD · SATACMR-
Seagate IRONWOLF PRO ST10000NE0008 10TB SATA 7200 RPM 3.5 256MB 3.5 IN, ST10000NE0008 (RPM3.5 256MB 3.5IN)10 TB£495.00£49.50NAS HDD · SATACMR-
WD Red Pro 6TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache6 TB£297.99£49.67NAS HDD · SATACMR-
Seagate IronWolf Pro, 6 TB, Enterprise NAS Internal HDD –CMR 3.5 Inch, SATA 6 Gb/s, 7,200 RPM, 256 MB Cache for RAID Network Attached Storage, 3 year Rescue Services (ST6000NT001)6 TB£298.49£49.75Enterprise HDD · SATACMREnterprise-
Seagate 6TB IronWolf ST6000VN001 5400RPM 256MB NAS6 TB£299.00£49.83NAS HDD · SATACMR-
Seagate IronWolf Pro ST4000NE001 - HDD - 4 TB - Internal - 3.5" - SATA 6Gb/s - 7200 RPM - Buffer: 256 MB - with Piano di Assistenza Recupero Dati di Emergenza di 2 Anni4 TB£200.00£50.00NAS HDD · SATACMR-
WD Red Pro 8TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache, 5 Year Warranty8 TB£399.98£50.00NAS HDD · SATACMR-
WD Red Pro 6TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache, 5 Year Warranty6 TB£308.98£51.50NAS HDD · SATACMR-
WD Red Plus 4TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, CMR, 64MB Cache4 TB£209.01£52.25NAS HDD · SATACMR-
Synology DS223 24TB 2 Bay Desktop NAS Solution installed with 2 x 12TB Western Digital Red Plus Drives24 TB£1,253.99£52.25NAS HDD · SATACMR-
Western Digital WD40EFZX WD Red Plus 4TB SATA 6Gb/s 3.5" HDD4 TB£209.88£52.47NAS HDD · SATACMR-
WD Western Digital Red Plus 3.5" 4000 GB Serial ATA III4 TB£209.88£52.47NAS HDD · SATACMR-
Western Digital WD Red Plus 8TB SATA 6Gb/s 3.5" HDD8 TB£429.00£53.63NAS HDD · SATACMR-
WD Red Pro 4TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR, 256MB Cache4 TB£214.99£53.75NAS HDD · SATACMR-
Seagate Exos 7E10 4TB Internal Hard Drive HDD - 3.5 Inch 4Kn SAS 12GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST4000NM005B)Used4 TB£219.54£54.89Enterprise HDD · SASCMREnterprise-
Toshiba HDWQ140UZSVA - 4TB N300 NAS Internal HDD Bulk4 TB£220.00£55.00NAS HDD · SATACMR-
Synology DS423 32TB 4 Bay Desktop NAS Solution installed with 4 x 8TB Seagate Ironwolf Drives32 TB£1,781.00£55.66NAS HDD · SATACMR-
Seagate IronWolf Pro ST4000NT001 3.5" 4TB SATA4 TB£228.99£57.25NAS HDD · SATACMR-
Seagate IronWolf 4TB Internal Hard Drive, NAS HDD, 3.5 Inch, 5400 RPM, CMR, 256 MB Cache, SATA 6GB/s, Silver, Includes 3 Year Rescue Service, FFP, Model No.: ST4000VN0064 TB£231.69£57.92NAS HDD · SATACMR-
Western Digital Ultrastar DC HC310 HUS726T4TALE6L4 3.5" 4000 GB Serial ATA III4 TB£234.00£58.50Enterprise HDD · SATACMREnterprise-
WD Red Pro 4TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR Recording Technology, 256MB Cache4 TB£235.00£58.75NAS HDD · SATACMR-
Seagate Exos 7E10 4TB Internal Hard Drive HDD - 3.5 Inch 512e/4Kn SAS 6GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST4000NM000B)4 TB£235.47£58.87Enterprise HDD · SASCMREnterprise-
Synology DS423 24TB 4 Bay Desktop NAS Solution installed with 4 x 6TB Seagate Ironwolf Drives24 TB£1,447.99£60.33NAS HDD · SATACMR-
Seagate Exos 7E10 4TB Internal Hard Drive HDD - 3.5 Inch 4Kn SAS 12GB/s, 7.200 RPM, 256MB Cache and 2M MTBF for Enterprise, Data Centre (ST4000NM005B)4 TB£245.46£61.37Enterprise HDD · SASCMREnterprise-
WD Red Pro 4TB NAS 3.5" Internal Hard Drive - 7200 RPM Class, SATA 6 Gb/s, CMR Recording Technology, 256MB Cache4 TB£252.63£63.16NAS HDD · SATACMR-
Seagate IronWolf, 2TB, Enterprise Internal NAS HDD – CMR 3.5 Inch, SATA 6 Gb/s, 5900 RPM, 256 MB Cache for RAID NAS, Rescue Services (ST2000NT003)Used2 TB£130.78£65.39NAS HDD · SATACMR-
Western Digital WD30EFPX / 3 TB/Red Plus3 TB£199.99£66.66NAS HDD · SATACMRPrime
Seagate IronWolf 2TB, Enterprise Internal NAS HDD, CMR 3.5 Inch, SATA 6GB/s, 5900 RPM, 256MB Cache for RAID NAS, Data Rescue Services, Frustration Free Packaging (ST2000VNZ03)2 TB£139.99£70.00NAS HDD · SATACMRPrime
Synology DS423 16TB 4 Bay Desktop NAS Solution installed with 4 x 4TB Western Digital Red Plus Drives16 TB£1,119.99£70.00NAS HDD · SATACMR-
Synology DS423 16TB 4 Bay Desktop NAS Solution installed with 4 x 4TB Seagate Ironwolf Drives16 TB£1,124.00£70.25NAS HDD · SATACMR-
Seagate Technology Exos X20, 20TB, 3.5-Inch SATA Hard Drive at 6GB/s, 7,200 RPM, 2.5M MTBF, 512e and 4Kn FastFormat, Low Latency with Enhanced Cache (ST20000NM007D), Green20.2 TB£1,484.98£73.51Enterprise HDD · SATACMREnterprise-
Seagate EXOS 2TB Enterprise 2.5" SATA HDD/Hard Drive2 TB£149.00£74.50Enterprise HDD · SATACMREnterprise-
WD Red Plus 2TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6Gb/s, CMR, 64MB Cache2 TB£155.45£77.72NAS HDD · SATACMR-
Synology DS925+(2X 2.5GbE Ports, Ryzen V1500B, 4GB RAM) 4-Bay 32TB Bundle with 4X 8TB Seagate Ironwolf HDDs32 TB£2,506.44£78.33NAS HDD · SATACMRPrime
WD Red Plus 2TB NAS 3.5" Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, CMR, 128MB Cache2 TB£164.76£82.38NAS HDD · SATACMR-
Seagate IronWolf Pro 8 TB NAS Internal Hard Drive HDD – 3.5 Inch SATA 6 Gb/s 7200 RPM 256 MB Cache for RAID Network Attached Storage, Data Recovery Service (ST8000NE0004)8 TB£659.00£82.38NAS HDD · SATACMR-
Synology DS223 8TB 2 Bay Desktop NAS Solution installed with 2 x 4TB Seagate Ironwolf Drives8 TB£699.90£87.49NAS HDD · SATACMR-
WD Western Digital Red Plus 3.5" 2000 GB Series ATA III2 TB£176.99£88.50NAS HDD · SATACMR-
Seagate Exos 7E2000 ST1000NX0423 1TB Internal Hard Drive 2.5" SFF SATA 6Gbps NL 7200RPM Buffer 128MB1 TB£100.00£100.00Enterprise HDD · SATACMREnterprise-
Seagate Exos 10E2400 ST1800MM0129 - Hybrid hard drive - 1.8 TB (16 GB Flash) - internal - 2.5" SFF - SAS 12Gb/s - 10000 rpm - buffer: 256 MB1.8 TB£180.00£100.00Enterprise HDD · SASCMREnterprise-
WD Red SA500 2TB NAS SATA SSD 2.5 InchUsed2 TB£218.33£109.17NAS SSD · SATANASPrime
QNAP TS-233/4TB 2 Bay Dekstop NAS Unit with Seagate IronWolf Drives4 TB£529.99£132.50NAS HDD · SATACMR-
Synology DS223 4TB 2 Bay Desktop NAS Solution installed with 2 x 2TB Western Digital Red Plus Drives4 TB£539.99£135.00NAS HDD · SATACMR-
Gigastone 1TB NAS SSD Drive (2-Pack) 24/7 Durable TLC High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives2 TB£298.90£149.45NAS SSD · SATANAS-
Gigastone 4TB NAS SSD Drive 24/7 Durable High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives4 TB£598.99£149.75NAS SSD · SATANAS-
Gigastone 4TB NAS SSD Drive (2-Pack) 24/7 Durable High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives8 TB£1,296.90£162.11NAS SSD · SATANAS-
WD Red SA500 4TB NAS SATA SSD 2.5 Inch4 TB£699.00£174.75NAS SSD · SATANAS-
Gigastone 2TB NAS SSD Drive (4-Pack) 24/7 Durable TLC High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives8 TB£1,469.80£183.73NAS SSD · SATANAS-
Gigastone 512GB NAS SSD Drive (2-Pack) 24/7 Durable TLC High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives1.02 TB£208.90£204.00NAS SSD · SATANAS-
Gigastone 512GB NAS SSD Drive 24/7 Durable TLC High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives512 GB£115.99£226.54NAS SSD · SATANAS-
Gigastone 1TB NAS SSD Drive 24/7 Durable TLC High Endurance RAID Data Storage Network Attached Storage 2.5" SATA Internal Solid State Hard Drives1 TB£239.99£239.99NAS SSD · SATANAS-
WD Red 1 TB NAS SSD 2.5 Inch SATA1 TB£248.99£248.99NAS SSD · SATANASPrime

Frequently asked questions

Why is SMR bad for RAID rebuilds?

Rebuilding writes a long, continuous stream of data to the replacement drive, which is the sustained-write workload SMR handles worst. The drive slows dramatically once its cache fills, and the rebuild can take so long that the RAID controller marks the drive as unresponsive and drops it, causing the rebuild to fail.

How do I tell if a drive is CMR or SMR?

Manufacturers do not always label it clearly, so check the exact model number against the maker's published CMR/SMR list or a community reference. As a rule, drives marketed specifically for NAS, such as IronWolf, WD Red Plus and Red Pro, Exos and N300, are CMR, while cheap desktop and external drives are often SMR.

Which WD Red drives are SMR?

Plain WD Red in the 2 to 6TB range using EFAX model numbers used SMR and is best avoided in RAID. WD Red Plus and WD Red Pro are CMR and are the correct choices for a NAS. Always confirm the exact model before buying a WD Red.

Is SMR ever acceptable in a NAS?

Only outside RAID. A single SMR drive used as a cold archive or an occasional backup target, with mostly reads and light writes, can be fine. The moment a drive joins a RAID array and might need to rebuild, you want CMR.

Does mixing one SMR drive into a CMR array cause problems?

It can. The SMR drive becomes the weak link during writes and especially during a rebuild, where its slow sustained-write speed can stall or fail the operation. Keep every drive in a RAID array CMR for predictable behaviour.

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