From mboxrd@z Thu Jan 1 00:00:00 1970 From: hpa@zytor.com (H. Peter Anvin) Subject: Re: Call for RAID-6 users Date: Thu, 5 Aug 2004 23:51:16 +0000 (UTC) Sender: linux-raid-owner@vger.kernel.org Message-ID: References: <200407302311.04942.maarten@ultratux.net> <200407302338.33823.maarten@ultratux.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Followup to: <200407302338.33823.maarten@ultratux.net> By author: maarten van den Berg In newsgroup: linux.dev.raid > > On Friday 30 July 2004 23:11, maarten van den Berg wrote: > > On Saturday 24 July 2004 01:32, H. Peter Anvin wrote: > > > 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