Resilvering speed gradually slowing down

[mnt_schred]

I am resilvering 4,88 T data which is gradually slowing down.

The rate started with 127 M/s, 10 h but now has slowed down to 18,2 M/s and slowing.
Is there any way to increase the speed? Any reason why it would slow down?
Can the resilvering process be paused and resumed?

 

[cyberjock]

It slows down as it progresses probably because hard drive transfer rates slow down as you traverse the platter.

AFAIK the resilvering cannot be paused and resumed. If you want to increase the speed you need to fix whatever your bottleneck is. Might be your hard drives, might be your CPU, you might need more RAM. It's tough to say. You'd have to experiment by replacing/upgrading each to see what happens.

 

[mnt_schred]

okay, the hard drive transfer rates slow down as you traverse the platter . By what physical process is this caused? Will the transfer rate stabilize at some point (now at 16.1 M/s, 84h36m to go) or will it continue to decrease?

If the percentage (4.36) is the variable correlating to decrease is speed it will take a loooooong time i'm afraid.

 

[cyberjock]

The rate of sectors/sec past the head decreases as you go from the outer tracks to the inner tracks. It's a physical characteristic of the hard disks and there is nothing you can do about it. Basically an outer "ring" is larger(has more sectors) than an inner "ring"(less sectors). Less sectors means slower performance.

If you are doing other things on the server while resilvering that will slow you down alot too. It's not uncommon for some people to claim it took a week to resilver a drive.

What's your hardware?

 

[paleoN]

Will the transfer rate stabilize at some point (now at 16.1 M/s, 84h36m to go) or will it continue to decrease?

It very well could go back up. Particularly considering you have 2 other disks you need to replace. If it's having trouble reading spots on those disks it will slow everything else down.

 

[mnt_schred]

Okay. an update on this: the resilvering process was finished faster then reported. If you are lucky, not the wole fs has to be scanned in order to resilver a disk succesfully.
Ill report back when I have replaced all disks.

A very important discovery is that the resilvering process CAN be restarted (!).
If you shutdown the machine during resilver and restart it, it WILL pick up where it left. :)

 

[Stephens]

A very important discovery is that the resilvering process CAN be restarted (!).
If you shutdown the machine during resilver and restart it, it WILL pick up where it left. :)

ZFS FTW. I'm still in favor of a UPS for a NAS, but ZFS is amazingly resiliant.