From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Distributed spares Date: Mon, 13 Oct 2008 17:50:25 -0400 Message-ID: <48F3C2A1.3080607@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Linux RAID List-Id: linux-raid.ids Over a year ago I mentioned RAID-5e, a RAID-5 with the spare(s) distributed over multiple drives. This has come up again, so I thought I'd just mention why, and what advantages it offers. By spreading the spare over multiple drives the head motion of normal access is spread over one (or several) more drives. This reduces seeks, improves performance, etc. The benefit reduces as the number of drives in the array gets larger, obviously with four drives using only three for normal operation is slower than four, etc. And by using all the drives all the time, the chance of a spare being undetected after going bad is reduced. This becomes important as array drive counts shrink. Lower cost for drives ($100/TB!), and attempts to drop power use by using fewer drives, result in an overall drop in drive count, important in serious applications. All that said, I would really like to bring this up one more time, even if the answer is "no interest." -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark