From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: Help: very slow software RAID 5. Date: Fri, 21 Sep 2007 01:08:41 +0400 Message-ID: <46F2E159.9030806@msgid.tls.msk.ru> References: <20070918230914.9FF5910215F@medulla.enet.sharplabs.com> <20070919014919.DF19D10215F@medulla.enet.sharplabs.com> <20070919174956.9497310209D@medulla.enet.sharplabs.com> <46F292E2.1090700@tmr.com> <20070920184738.441FD10208C@medulla.enet.sharplabs.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070920184738.441FD10208C@medulla.enet.sharplabs.com> Sender: linux-raid-owner@vger.kernel.org To: "Dean S. Messing" Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Dean S. Messing wrote: [] > [] That's what > attracted me to RAID 0 --- which seems to have no downside EXCEPT > safety :-). > > So I'm not sure I'll ever figure out "the right" tuning. I'm at the > point of abandoning RAID entirely and just putting the three disks > together as a big LV and being done with it. (I don't have quite the > moxy to define a RAID 0 array underneath it. :-) "Putting three disks together as a big LV" - that's exactly what "linear" md module. It's almost as unsafe as raid0, but with linear read/write speed equal to speed of single drive... Note also that the more drives you add to raid0-like config, the more chances of failure you'll have - because raid0 fails when ANY drive fails. Ditto - for certain extent - for linear md module and for "one big LV" which is basically the same thing. By the way, before abandoming "R" in "RAID", I'd check whenever the resulting speed with raid5 (after at least read-ahead tuning) is acceptable, and use that if yes. If no, maybe raid10 over the same 3 drives will give better results. /mjt