Re: RAID6 syncing at 24 MB/s?

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 1630 bytes --]

On 18 Apr 2012 01:22:35 -0400 "George Spelvin" <linux@horizon.com> wrote:

> > Can you try an experiment for me (if you don't have anything useful on the
> > array yet)?
> > 
> > Stop the array.  Recreate it exactly the same way as before, and see if it
> > goes faster.  I think it might - at least until it got up to where it was up
> > to.
> 
> Um, unfortunately, I do (I didn't actually make the posting until after
> the sync finished), but it should actually be non-destructive to do that
> to an existing array, right?
> 
> It's just like deleting and re-creating a partition; as long as you're
> *damn* sure you kept the parameters the same, it's a no-op.  Right?

Should be - yes.  But some times it is best not to play with fire.
Up to you....

Alternately, look at /proc/diskstats for the member devices.

The first 4 numbers relate to reads (iOs, Merges, Sectors, ticks) and the next
4 to writes.

You will probably see about  3 times as many reads as writes.

RAID6 resync reads the whole stripe, checks the parity blocks, and if they
are wrong it writes them out.

If most of them are good - you should see streaming writes at the full speed
of the disk/bus/slowest-part.

If lots are not correct (which can be expected on a new array), you get lot
of 
    read - seek-backwards - write

sequences, which slow things down a lot.

NeilBrown


> 
> I still have the data on the backup drives, so it's "only" a day's
> lost work if I fry it (I did some reorganization as well as simple bulk
> copying), so it's not *deadly* dangerous...
> 
> Thank you for the response!


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 828 bytes --]