Re: Call for RAID-6 users

Followup to:  [ref]
By author:    maarten van den Berg [off-list ref]
In newsgroup: linux.dev.raid

On Friday 30 July 2004 23:11, maarten van den Berg wrote:

quoted

On Saturday 24 July 2004 01:32, H. Peter Anvin wrote:

quoted

I'm still early in the testing phase, so nothing to report as yet.
But I have a question:  I tried to reproduce a reported issue when creating
a degraded raid6 array.  But when I created a raid6 array with one disk
missing, /proc/mdstat reported no resync going on.  Am I not correct in
assuming that raid6 with 1 missing drive should at least start resyncing
the other drive(s) ?  It would only be really degraded with two missing
drives...

So instead, I defined a full raid6 array which it is now resyncing...
My resync speed is rather slow (6000K/sec). I'll have to compare it to
resyncing a raid5 array though before concluding anything from that.  Cause
this system is somewhat CPU challenged indeed: a lowly celeron 500.

To confirm, after stopping the raid6 array (didn't want to wait this long) I 
created a raid5 array on the same machine and it resyncs at 14000K/sec.
Is this expected behaviour, the 6M/sec for raid6 vs 14M/sec for raid5 ?
I suppose raid6 has to sync two drives, which would maybe explain the speed 
difference(?)   In any case, hdparm -tT report 50M/sec on each single drive. 
Is this discrepancy in speed normal ?
(yes yes, I played with the /proc/sys/dev/raid/ speed settings (to no avail))

A newly created RAID-5 array uses a special trick to do the initial
sync faster.  Unfortunately that trick is not possible for RAID-6.

	-hpa