From mboxrd@z Thu Jan 1 00:00:00 1970 From: mru@kth.se (=?iso-8859-1?q?M=E5ns_Rullg=E5rd?=) Subject: Re: RAID1 over RAID0 misbehavior Date: Wed, 07 Jan 2004 21:22:49 +0100 Sender: linux-raid-owner@vger.kernel.org Message-ID: References: <20040107200951.GB5143@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Jose Luis Domingo Lopez writes: > On Wednesday, 07 January 2004, at 01:37:20 +0100, > M=E5ns Rullg=E5rd wrote: > >> I recently created a RAID1 mirror from two identical RAID0 arrays >> under Linux 2.6.0. I was surprised when /proc/mdstat reported a >> resync speed of 1 MB/s, even though the system was otherwise idle. = I >> > Anyways, it seems wiser to make two RAID1 arrays and then a RAID0 fro= m > them two. Apart from (maybe) preventing the problem you are > experiencing, this should give you better results in the case of a dr= ive > failure, when it happens. > > Think for a moment about the event of a single hard drive failure: wi= th > two RAID1 arrays, one of then will go to degraded mode, but as far as= I > know the upper RAID0 will not notice a thing, so will continue workin= g > as usual, maybe with a little performance decrease. > > On the other hand, if you have two RAID0 arrays and one of the hard > drives fail, the RAID0 where it happens will fail, the upper RAID1 wi= ll > run degraded, and when a new disk replaces the failed one you will ha= ve > to start the failed RADI0 again, and let the upper RAID1 reconstruct > itself. I think this situation is worse than the one depicted before. > > Am I missing something ? I had a few reasons: - I read somewhere that RAID0 over RAID1 didn't work. Maybe this information was outdated. - I was short on spare disks, so I had to build an initially degraded array and then add the other half of the mirror. - Performance after a disk failure isn't a big issue with this machine. Resyncing takes only an hour or two anyway. --=20 M=E5ns Rullg=E5rd mru@kth.se - To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html