From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: question about the best suited RAID level/layout Date: Thu, 04 Jul 2013 17:43:38 -0400 Message-ID: <51D5EC8A.40509@turmel.org> References: <1372961877.8716.43.camel@heisenberg.scientia.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1372961877.8716.43.camel@heisenberg.scientia.net> Sender: linux-raid-owner@vger.kernel.org To: Christoph Anton Mitterer Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/04/2013 02:17 PM, Christoph Anton Mitterer wrote: > Hi. > > I'm setting up a 5-bay NAS (based on a QNAP device), with my personal > Debian on it, currently using only 4 devices though > The focus is absolutely on data security/resilience,... and not at all > on performance. This particular statement trumps all other considerations. > Now questions comes, which RAID level to use, and I guess with the main > focus on resilience there's only basically these options: [snip /] You covered all the basics. >From your own analysis, raid6 is the option that maximizes total storage while achieving an "any two failures" resiliency. Triple-copy raid10 across four drives can match that resiliency, with dramatically better performance, but with a substantial cost in capacity. Two-failure resilience is vital to completing recovery after replacing a failed drive, particularly when the read error rates of consumer-grade drives are involved. In your specific case, raid6 has one additional advantage: making future expansion to the fifth bay a reliable, simple, no downtime event. In your situation, I would use raid6. To mitigate the performance hit on occasional random-access work, I would use a small chunk size (I use 16k). That will somewhat hurt peak linear performance, but even bluray-equivalent media streams only amount to 5 MB/s or so. That would be 80 IOPS per device in such a four-drive raid6. Phil