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SubjectRe: Raid5 resync slow with one linear array
On Thu, Apr 04, 2002 at 02:03:16PM +1000, Neil Brown wrote:
> On Monday April 1, mfedyk@matchmail.com wrote:
> > Hi,
> >
> > I just setup a 4 (5 really) drive raid5 array.
> >
> > It is syncing up right now and nothing else is running on the system.
> >
> > I have three 18GB SCA scsi drives and 2x9GB linear array in a four "drive"
> > raid5 array.
> >
> > Unfortunately, it is syncing up quite slowly. Only about 2MB/sec on a
> > 40MB/sec array. The system is idle.
> >
> > 2.4.19-pre4-ac3
> >
> > Is there something about this config that says "Don't do that!"? I've
> > heard about RAID10, but not Linear+RAID5...
>
> echo 10000 > /proc/sys/dev/raid/speed_limit_min
>
> md tries to monitor the activity on the component devices and limits
> rebuild activity when there appears to be other activity.
> It measures "other activity" as "blocks added to kstat.dk_drive_?blk",
> minus "block due to resync activity".
>
> When a component device is an md array, nothing gets recorded
> in kstat, but lots is recorded as resync activity, so this "other
> activity" appears as a negative number which, due to storage in an
> unsigned long, appears rather large.
>
> NeilBrown

Yeah, thought it was something like that. Thanks for the explanation. I
didn't see your message until I sent the other one.

Mike
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