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

[Chris Heerschap <ChrisMH@AWeber.com>]

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.


cmh

On 3/4/13 7:36 PM, Eric at Lucii.org 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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