Forum Discussion

Luminary

Nov 17, 2024

RAID-5 vs RAID-6 rebuild speed

I have been upgrading disks in my various ReadyNAS units. The 4 bay units are RAID-5 and the 6 bay units are RAID-6. I haven't really seen it discussed here, so I thought I would point out that ...

Installation & Upgrade

Performance

Sandshark

Sensei - Experienced User

Nov 18, 2024

The speed of the drives is likely the controlling factor.

Laserbait
Luminary
Nov 18, 2024
I would have thought so too, but both arrays are using the same Seagate 7200 RPM 4TB disks, and both are upgrading to the same Hitachi 7200 RPM 10TB disks. The only difference between the two is the faster CPU, 2 more disks and RAID-6 on the RN316. And it doesn't seem to matter if it's the 1st drive, or the last drive to be replaced, it's always about the same rebuild speed.

I'm tempted to blow the RN316 array away, and start over with 4 x 4TB drives in a RAID-5. Once complete, replace one 4TB with a 10TB and see what the rebuild rate is. If it's closer to 90+MB/s, it's the RAID level.
- StephenB
  Guru - Experienced User
  Nov 18, 2024
  If you have ssh enabled you could enter
  
  sysctl dev.raid.speed_limit_min
  
  You should see that it is set to 30000, which is what you are getting with the RAID-6 rebuild.
  
  You could then try
  
  sysctl -w dev.raid.speed_limit_min=100000
  
  and see if that speeds it up.
  
  Probably best to set it back to 30000 when you are done with this.