From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Knecht Subject: mdadm RAID and drives spinning up/down Date: Sun, 21 Mar 2010 14:40:02 -0700 Message-ID: <5bdc1c8b1003211440n7e0b7848s7c069c3394d487a3@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Sender: linux-raid-owner@vger.kernel.org To: Linux-RAID List-Id: linux-raid.ids I'm moving forward on my first machine using RAID. This will be a fairly lightly used home server storing MythTV recordings and backups coming from other Linux machine. Due to the light workload I expect there will be times, sometimes lasting hours or maybe days, when the drives are unused and might (should?) spin down. Additionally with everyone trying to save power and be 'green' more and more drives probably do this by design anyway. OK, so never having build a RAID array and knowing nothing about this I'm curious about how mdadm handles this sort of thing. If the drives, using something like hdparm to set parameters, have times that shut them down for a while, when the system needs them spinning again are there ways to buffer write data and delay read data until everything is ready to roll again? I.e. - it's the middle of the night and Myth wants to start a recording. Everything is shut down and not it needs to start. Is it a problem if one drive spins up more slowly? Could that fool the RAID software into thinking the drive has died when it's actually just asleep? Sorry for such newbish questions. Thanks, Mark