Re: Raid5 resync slow with one linear array

[Mike Fedyk]

On Thu, Apr 04, 2002 at 02:03:16PM +1000, Neil Brown wrote:
> On Monday April 1, [e-mail] 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