How long does a Synology RAID rebuild take?
Typically several hours to a couple of days, depending on drive capacity, RAID type and how busy the NAS is. As a rough guide it scales with the size of the drives: larger drives take proportionally longer. The array stays usable during the rebuild but has reduced or no fault tolerance until it finishes.
Last verified July 22, 2026 · 1 official source checked Updated
This is a floor, not a promise: it assumes the drive reads or writes flat-out at the rate you set, with nothing else happening. Real rebuilds run longer: parity computation, using the NAS during the rebuild, and drive throttling all add time, and an SMR drive can multiply it. Sustained rates for current 3.5-inch NAS drives run roughly 180–280 MB/s (see each drive’s datasheet); 200 MB/s is a reasonable middle default.
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A rebuild (Synology calls it a repair) copies parity and data onto the replacement drive to restore redundancy. There is no single number, but the drive capacity is the main driver: a rebuild reads or writes across the whole array, so bigger drives mean a longer rebuild, often measured in hours per terabyte.
What affects the time
- Capacity: the dominant factor; a 4 TB rebuild is far quicker than a 20 TB one.
- RAID type: RAID 6/SHR-2 rebuilds involve double parity and can take longer than RAID 5/SHR.
- Load: if you keep using the NAS heavily during the rebuild, it slows down; leaving it idle speeds it up.
- Drive health: a struggling drive with slow reads drags the whole rebuild.
The risk window
While rebuilding, a single-parity array (RAID 5/SHR) has no remaining fault tolerance: a second drive failing before the rebuild finishes crashes the pool. That is exactly why large arrays of big drives lean toward RAID 6 or SHR-2: the rebuild takes longer, and double parity keeps you protected through it. You can keep using the NAS during a rebuild, but avoid heavy writes and do not remove any other drive.
Speeding it up
Leave the NAS as idle as possible, ensure good cooling, and use healthy CMR drives (an SMR replacement can massively lengthen a rebuild). If a rebuild seems stuck for days on a modest array, check the replacement drive's health.
Drives that solve this
Live Amazon.ca prices in CAD, ranked by price per terabyte. The Recording column is verified against manufacturer documentation. Prices checked
| Model | Capacity | Recording | Price | CA$/raw TB | |
|---|---|---|---|---|---|
 Seagate Exos X22 22TB SATA 6Gb/s 7200RPM 3.5" Enterprise Hard Drive - ST22000NM001ENewbest price per TB CMR recording, SATA enterprise drive Amazon.ca · sold by ServerPartDeals · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,108Buy on Amazon | 22 TB | CMR ✓ | CA$1,108 | CA$50.38/TB | Buy on Amazon |
 Seagate IronWolf Pro 32TB Enterprise NAS Internal HDD Hard Drive – CMR 3.5 Inch SATA 6Gb/s 7200 RPM 512MB Cache for RAID Network Attached Storage, Rescue Services (ST32000NTZ00)New CMR recording, SATA NAS drive rated for 24/7 use Amazon.ca · sold by THEKEYKEY · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,740Buy on Amazon | 32 TB | CMR ✓ | CA$1,740 | CA$54.37/TB | Buy on Amazon |
 Seagate Exos M 28TB Enterprise Internal Hard Drive HDD - 3.5in 6GB/s SATA 7200RPM 2.5M MTBF (ST28000NM003K)New CMR recording, SATA enterprise drive Amazon.ca · sold by Amazon.ca · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,543Buy on Amazon | 28 TB | CMR ✓ | CA$1,543 | CA$55.11/TB | Buy on Amazon |
 Seagate IronWolf 10TB NAS Internal Hard Drive HDD – CMR 3.5 Inch SATA 6Gb/s 7200 RPM 256MB Cache for RAID Network Attached Storage (ST10000VN0008) (ST10000VNZ008/N0008)New CMR recording, SATA NAS drive rated for 24/7 use Amazon.ca · sold by Deals2You · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$579Buy on Amazon | 10 TB | CMR ✓ | CA$579 | CA$57.91/TB | Buy on Amazon |
 Seagate Exos X24 ST20000NM002H 20TBNew CMR recording, SATA enterprise drive Amazon.ca · sold by THEKEYKEY · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,165Buy on Amazon | 20 TB | CMR ✓ | CA$1,165 | CA$58.25/TB | Buy on Amazon |
 Western Digital HUH721212ALE604 12TB Ultrastar DC HC520 SATA HDD - 7200 RPM Class, SATA 6 Gb/s, 256MB Cache, 3.5"New CMR recording, SATA enterprise drive Amazon.ca · sold by Seller_King · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$699Buy on Amazon | 12 TB | CMR ✓ | CA$699 | CA$58.25/TB | Buy on Amazon |
 Seagate Exos X24 24TB Enterprise Internal Hard Drive HDD - 6GB/s SATA 7200RPM 2.5M MTBF (ST24000NM002H)New CMR recording, SATA enterprise drive Amazon.ca · sold by THEKEYKEY · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,400Buy on Amazon | 24 TB | CMR ✓ | CA$1,400 | CA$58.33/TB | Buy on Amazon |
 Toshiba N300 PRO 8TB Large-Sized Business NAS (up to 24 Bays) 3.5-Inch Internal Hard Drive - Up to 300 TB/Year Workload Rate CMR SATA 6 GB/s 7200 RPM 512 MB Cache - HDWG780XZSTBNew CMR recording, SATA NAS drive rated for 24/7 use Amazon.ca · sold by HYPER MEGA Electronics · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$480Buy on Amazon | 8 TB | CMR ✓ | CA$480 | CA$60.00/TB | Buy on Amazon |
 Seagate IronWolf Pro 20TB Enterprise NAS Internal HDD Hard Drive – CMR 3.5 Inch SATA 6Gb/s 7200 RPM 256MB Cache for RAID Network Attached Storage, Rescue Services (ST20000NTZ01/ST20000NT001)New CMR recording, SATA NAS drive rated for 24/7 use Amazon.ca · sold by THEKEYKEY · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,235Buy on Amazon | 20 TB | CMR ✓ | CA$1,235 | CA$61.75/TB | Buy on Amazon |
 Western Digital 22TB WD Red Pro NAS Internal Hard Drive HDD - 7200 RPM, SATA 6 Gb/s, CMR, 512 MB Cache, 3.5" - WD221KFGXNew CMR recording, SATA NAS drive rated for 24/7 use Amazon.ca · sold by Deals2You · one bare internal drive; shipping and taxes not included · checked Oct 7, 2026CA$1,400Buy on Amazon | 22 TB | CMR ✓ | CA$1,400 | CA$63.64/TB | Buy on Amazon |
Related questions
- Why is my RAID rebuild taking days?
- How long does it take to rebuild an 8TB drive in a NAS?
- How long does it take to rebuild a 12TB drive in a NAS?
- How long does it take to rebuild a 16TB drive in a NAS?
- Can SMR drives be used in RAID?
- Is my data safe if one drive fails in RAID 5?
- Can I replace a failed Synology drive with a bigger one?
- Can I hot swap a drive in a Synology NAS?
Sources
Every technical claim on this page is checked against manufacturer and standards documentation. Dates are when each source was last reviewed.
- Synology KB: Repair a Storage Pool (checked 2026-07-22)