[CentOS] variable raid1 rebuild speed?

Thu Jan 13 22:55:29 UTC 2011
Brian Mathis <brian.mathis at gmail.com>

On Thu, Jan 13, 2011 at 8:56 AM, Les Mikesell <lesmikesell at gmail.com> wrote:
> On 1/13/11 5:58 AM, Kevin Thorpe wrote:
>> On 12/01/2011 18:38, Les Mikesell wrote:
>>> I have a 750Gb 3-member software raid1 where 2 partitions are always
>>> present and the third is regularly rotated and re-synced (SATA disks in
>>> hot-swap bays).  The timing of the resync seems to be extremely variable
>>> recently, taking anywhere from 3 to 10 hours even if the partition is
>>> unmounted and the drives aren't doing anything else and regardless of
>>> what I echo into /proc/sys/dev/raid/speed_limit_min or _max.  Is there
>>> some way to tell if the drives are going bad or speed it up consistently
>>> if they aren't?
>> Ummmm.... RAID is not a backup policy. Fine use hotswap and rsync or
>> similar but you
>> really shouldn't be relying on raid rebuilds for that.
> These are backups to begin with.  It is the archive disk for backuppc which
> contains millions of hardlinked files for the de-duplication it uses. It would
> probably take a week or more for rsync to complete a copy (I've tried, but could
> never leave it offline long enough for any file-oriented copy approach to
> finish).  A raid sync should complete in the time it takes for one pass across
> the disk and does not require unmounting except momentarily while failing the
> member out.  I don't see why this is not a good use of raid rebuilds (the
> offsite members are rotated so the one being rebuilt is not the only copy). It
> used to always complete in 2 or 3 hours.   I would just like to know why it
> sometimes takes much longer.
> A related issue is that I'd like to use a laptop sized drive for the offsite
> copy and have one that has the same capacity.  However it uses 4k sectors and
> runs about 10x slower even though read speed is the same.  I understand that
> using a newer kernel and offsetting the start of the partition to a 4k boundary
> should fix this but I obviously can't do that with the existing raid. Does
> anyone have experience with the new drives with 4k sectors on Centos, or know if
> it will be addressed in Centos6?
> --
>   Les Mikesell
>     lesmikesell at gmail.com

I experimented with using disk image files mounted through loopback
for the BackupPC store.  It seemed to work but I didn't get much
further than testing.  It might be a way to use backuppc, and also be
able to file-copy the backups by copying the container file after it's
been unmounted.  If it's big, it won't be fast, but faster than
waiting for rsync to work out all the hard links.