[storage-discuss] approximately resilver time

[Bob Friesenhahn]

On Mon, 19 Oct 2009, borov wrote:

> Thinking about ZFS storage. I wish to know, that to expect.
> What approximately resilver time after disk failure on 8+2 raidz2. 
> Disks is 7200 SATA 1Tb. 2Tb will be interesting too.

The resilver time depends on how much data there is to be resilvered, 
the typical file sizes, filesystem blocksize, and the degree of 
fragmentation.  It also depends on the sequential read rate from each 
disk, as well as average seek time.  The resilver time then depends on 
the average data rate during resilvering (for your hardware) and the 
amount of data to be resilvered.

This is the math I used in 'bc' for 20MB/second and 1TB to be 
resilvered:

% bc
scale=2
((1000*1000*1000*1000)/(20*1000*1000))/(60*60)
13.88

So we get these results:

Resilver Rate	Hours
20MB/second	13.88
30MB/second:	9.25
40MB/second:	6.94
50MB/second:	5.55
60MB/second:	4.62
70MB/second:	3.96
80MB/second:	3.47

You may want to search the zfs-discuss list for reports of typical 
resilver rates.  From what I have seen posted by others, resilver 
rates for raidz2 with SATA disks tend to be low.

Bob
--
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/