Chris Heerschap on 5 Mar 2013 06:58:29 -0800

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Re: [PLUG] Survey: Linux RAID mirror sync time

That's a pretty open-ended question, and the best response to that is "it depends".

I've seen rebuilds go quickly when done with fast, small SAS/SCSI disks. I've seen them go slowly with larger SATA disks. For example, on a dedicated storage system (IBM DS4500) we saw an 8 hour rebuild time on a 500GB SATA disk. Larger disks took a proportionally longer time. Unless the system is loaded, the rebuild time shouldn't change much either way based on the CPU type.

Conversely, a mirror rebuild on SSD should be really, really quick.

Big, slow SATA drives are part of the reason why more redundant arrays like RAID-6 (or RAIDZ2 and RAIDZ3 on ZFS) are gaining popularity - rebuilds of really big disks can take so long that the possibility of a second drive fault goes up significantly. Drives are faster than old PATA drives, but also *significantly* bigger.


On 3/4/13 7:36 PM, Eric at wrote:
Just curious what folk's experience is with this.
If you replace one drive of a RAID mirror pair with
a blank drive how long does it take to sync?

Maybe 5 years ago I replaced a 160GB drive in such a
configuration and as I recall the sync was about 2 hours.
That was a 500 MHz Celeron with PATA drives.

I believe that faster drives (SATA and even SAS) and
faster chip sets and bus speeds may cancel out the
penalty of larger drive sizes.  I only ever had to
sync a drive that one time so the data sample size is
way too small :-)

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