CMR vs SMR Drives for NAS: Why It Matters More Than Brand
Compatibility data on this site last refreshed 2026-11-03 · reading time ~3 min
CMR (conventional magnetic recording) and SMR (shingled magnetic recording) describe how a hard drive writes data. For desktop use the difference barely shows. In a NAS — where drives run 24/7 in RAID — it decides whether your array survives its first rebuild.
The problem with SMR in a NAS
SMR drives overlap write tracks like roof shingles to squeeze more capacity onto platters. Random writes and long sustained writes force the drive to re-shingle data, causing write speeds to collapse from ~180MB/s to under 10MB/s for minutes at a time. During a RAID rebuild — exactly when a second drive failing kills the array — that stall can stretch a 10-hour rebuild into days.
Which drive lines are CMR
- Seagate IronWolf and IronWolf Pro: CMR across the line
- WD Red Plus, Red Pro and Gold: CMR
- Toshiba N300 and MG series: CMR
- WD Red (non-Plus): mixed — several part numbers (e.g. the 2-6TB EFAX models) are SMR; check the exact part number before buying
- Desktop lines (WD Blue, Barracuda, Toshiba P300): mostly SMR at 2TB+ — avoid in multi-bay NAS
How to check a specific drive
Search the exact part number, not the marketing name. Synology's official compatibility list doesn't label CMR/SMR, so verify on the vendor's datasheet — or open the drive's page here and check its series: every NAS-tuned series listed on this site (IronWolf, Red Plus, Red Pro, N300, MG, Exos, Gold) is CMR.
CMR vs SMR lookup: check your part number
The table and search below cover every part number in the compatibility lists we track — 49 rated series-level entries across 3,108 part numbers. Search any part number to see whether its series is rated CMR, mixed, or unrated. Series with a manufacturer CMR rating are safe for NAS arrays and cold copies; the mixed ones (WD Red is the classic case) vary by exact part number, so verify before buying.
CMR vs SMR lookup: 795 rated series, 3108 part numbers
The table lists every drive series where the manufacturer's own rating is on file — shingled (SMR) or mixed-series first, because those are the ones that hurt a NAS. Search any part number below for its rating; parts with no rating on file are labelled as such rather than guessed.
| Brand | Series | Recording (manufacturer rating) | Rated parts | Example part numbers |
|---|---|---|---|---|
| Western Digital | Red | Mixed CMR/SMR — varies by exact part number | 27 | WD100EFAX - 68LHPN0, WD101EFAX - 68LDBN0, WD10EFRX - 68JCSN0 |
| Western Digital | WD RED | Mixed CMR/SMR — varies by exact part number | 3 | WD101EFAX, WD120EFAX, WD80EFRX/ EFAX |
| Seagate | Constellation ES | CMR — safe for NAS arrays | 1 | ST31000425SS |
| Seagate | Constellation ES.3 | CMR — safe for NAS arrays | 12 | ST1000NM0033, ST1000NM0053, ST2000NM0023 - 9ZM275 |
| Seagate | EXOS 7E10 | CMR — safe for NAS arrays | 33 | ST10000NM017B-2TL103, ST10000NM018B-2TL203, ST10000NM018B |
| Seagate | EXOS X24 | CMR — safe for NAS arrays | 11 | ST10000NM021H, ST12000NM002H, ST12000NM007H |
| Seagate | Enterprise NAS HDD | CMR — safe for NAS arrays | 13 | ST2000NE0015, ST2000VN0001 - 1SF174, ST2000VN0011 - 1UL174 |
| Seagate | Exos 7E10 | CMR — safe for NAS arrays | 14 | ST10000NM017B, ST10000NM020B - 2TL213, ST2000NM001B |
| Seagate | Exos 7E2 | CMR — safe for NAS arrays | 2 | ST1000NM0008, ST2000NM0008 - 2F3100 |
| Seagate | Exos 7E8 | CMR — safe for NAS arrays | 38 | ST1000NM000A, ST2000NM000A, ST2000NM001A |
| Seagate | Exos X10 | CMR — safe for NAS arrays | 5 | ST10000NM0016 - 1TT101, ST10000NM0016, ST10000NM0086 |
| Seagate | Exos X12 | CMR — safe for NAS arrays | 3 | ST12000NM0007 - 2A1101, ST12000NM0007, ST12000NM0027 - 2A1201 |
| Seagate | Exos X14 | CMR — safe for NAS arrays | 7 | ST10000NM0478, ST10000NM0528 - 2H7200, ST12000NM0008 |
| Seagate | Exos X16 | CMR — safe for NAS arrays | 9 | ST10000NM001G - 2MW103, ST10000NM002G - 2MU203, ST12000NM001G - 2MV103 |
| Seagate | Exos X18 | CMR — safe for NAS arrays | 6 | ST10000NM018G, ST14000NM008J, ST16000NM005J |
| Seagate | Exos X20 | CMR — safe for NAS arrays | 2 | ST20000NM000D, ST20000NM007D - 3DJ103 |
| Seagate | Exos X24 | CMR — safe for NAS arrays | 2 | ST20000NM002H - 3KV133, ST24000NM002H - 3KS133 |
| Seagate | IronWolf | CMR — safe for NAS arrays | 91 | ST10000VN000 - 3AK101, ST10000VN000, ST10000VN0004 - 1ZD101 |
| Seagate | IronWolf Pro | CMR — safe for NAS arrays | 123 | ST10000NE000 - 3AP101, ST10000NE000, ST10000NE0004 - 1ZF101 |
| Seagate | NAS | CMR — safe for NAS arrays | 19 | ST10000VN0014, ST1000VN000, ST1000VN001 |
| Seagate | Surveillance | CMR — safe for NAS arrays | 26 | ST10000VX0014, ST1000VX000, ST1000VX001 |
| Toshiba | MG04ACA**** | CMR — safe for NAS arrays | 11 | MG04ACA100N, MG04ACA200A, MG04ACA200E |
| Toshiba | MG04SCA**** | CMR — safe for NAS arrays | 3 | MG04SCA200E, MG04SCA300E, MG04SCA400E |
| Toshiba | MG04SCA**E | CMR — safe for NAS arrays | 4 | MG04SCA20EE, MG04SCA40EE, MG04SCA50EE |
| Toshiba | MG05ACA**** | CMR — safe for NAS arrays | 1 | MG05ACA800E |
| Toshiba | MG06ACA**** | CMR — safe for NAS arrays | 3 | MG06ACA10TE, MG06ACA600E, MG06ACA800E |
| Toshiba | MG07ACA*** | CMR — safe for NAS arrays | 2 | MG07ACA12TE, MG07ACA14TE |
| Toshiba | MG08ACA*** | CMR — safe for NAS arrays | 1 | MG08ACA16TE |
| Toshiba | MG08SCA*** | CMR — safe for NAS arrays | 1 | MG08SCA16TE |
| Toshiba | MN04ACA*** | CMR — safe for NAS arrays | 1 | MN04ACA400 |
| Toshiba | MN05ACA*** | CMR — safe for NAS arrays | 2 | MN05ACA600, MN05ACA800 |
| Toshiba | MN06ACA*** | CMR — safe for NAS arrays | 3 | MN06ACA10T, MN06ACA600, MN06ACA800 |
| Toshiba | MN07ACA*** | CMR — safe for NAS arrays | 2 | MN07ACA12T, MN07ACA14T |
| Toshiba | MN08ACA*** | CMR — safe for NAS arrays | 1 | MN08ACA16T |
| Toshiba | N300 | CMR — safe for NAS arrays | 135 | HDWG11A*ZSTA, HDWG11AAZSTA, HDWG11AEZSTA |
| Toshiba | P300 | CMR — safe for NAS arrays | 16 | HDWD105AZSTA, HDWD105EZSTA, HDWD105UZSVA |
| Western Digital | Gold | CMR — safe for NAS arrays | 30 | WD1005FBYZ - 01YCBB1, WD1005FBYZ - 01YCBB2, WD1005FBYZ |
| Western Digital | Purple | CMR — safe for NAS arrays | 32 | WD100EJRX, WD100PURZ - 85W86Y0, WD101PURZ - 85C62Y0 |
| Western Digital | Red Plus | CMR — safe for NAS arrays | 17 | WD101EFBX - 68B0AN0, WD10EFRX (Red NASware 3.0), WD120EFBX - 68B0EN0 |
| Western Digital | Red Pro | CMR — safe for NAS arrays | 29 | WD101KFBX - 68R56N0, WD102KFBX - 68M95N0, WD102KFBX |
| Western Digital | Ultrastar 7K6 | CMR — safe for NAS arrays | 1 | HUS726T4TALA6L4 |
| Western Digital | Ultrastar DC HC320 | CMR — safe for NAS arrays | 5 | 0B36400 (HUS728T8TAL5204), HUS728T8TAL5201, HUS728T8TAL5204 - 0B36400 |
| Western Digital | Ultrastar DC HC330 | CMR — safe for NAS arrays | 3 | WUS721010AL5204, WUS721010ALE6L1, WUS721010ALE6L4 |
| Western Digital | Ultrastar DC HC510 | CMR — safe for NAS arrays | 12 | HUH721008AL5200 - 0F27356, HUH721008AL5204 - 0F27358, HUH721008ALE600 - 0F27455 |
| Western Digital | Ultrastar DC HC550 | CMR — safe for NAS arrays | 11 | WUH721814ALE6L1, WUH721814ALE6L4, WUH721816AL5204 |
| Western Digital | Ultrastar DC HC560 | CMR — safe for NAS arrays | 6 | WUH722020ALE6L1, WUH722020ALE6L4, WUH722020BL5201 |
| Western Digital | WD GOLD | CMR — safe for NAS arrays | 2 | WD242KRYZ, WD261KRYZ |
| Western Digital | WD RED Plus | CMR — safe for NAS arrays | 10 | WD101EFBX, WD120EFBX, WD140EFGX |
| Western Digital | WD RED Pro | CMR — safe for NAS arrays | 4 | WD161KFGX, WD181KFGX, WD201KFGX |
Search a part number
Quick answers
Is CMR really necessary for a 2-bay NAS?
It is strongly recommended even in 2-bay units. A 2-bay RAID 1 has zero redundancy during a rebuild — the exact scenario where SMR stalls hurt most.
Are all WD Red drives SMR?
No. WD Red Plus, Red Pro and Gold are CMR. Only some non-Plus WD Red part numbers (mainly 2-6TB EFAX variants) use SMR.
Does Synology block SMR drives?
No. Several SMR part numbers appear on Synology's official compatibility list, which is why checking CMR status yourself matters.
How do I check CMR vs SMR before buying a drive?
Search the exact part number in the lookup table on this page — it reflects the manufacturer's published series ratings for every drive in the official compatibility lists. If the series rating is mixed (like base WD Red), verify with the manufacturer's datasheet for that capacity; if no rating is on file, don't guess.
Check your exact model
Compatibility is per machine and per part number. Pick your model for its full official drive list: