From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: checking md device parity (forced resync) - is it necessary? Date: Tue, 05 Sep 2006 14:00:03 +0200 Message-ID: <44FD66C3.6040609@wpkg.org> References: <44FD3C65.8040000@wpkg.org> <17661.19907.140798.943518@cse.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <17661.19907.140798.943518@cse.unsw.edu.au> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: (...) >> Which starts a resync of drives. As one can imagine, resync of 800 GB on >> a rather slow device (600 MHz ARM) can take 12 hours or so... >> > > I believe that was intended to be once a month, not once a day. > Slight error in crontab. > >> So my question is: is this "daily forced resync" necessary? > > Daily is probably excessive, certainly on an array that size. > > Monthly is good. Weekly might be justified on cheap (i.e. unreliable) > drives and very critical data. > > With RAID, sleeping bad blocks can be bad. If you hit one while > recovering a failed drive, you have to put the piece back together by > hand. > A regular check can wake up those sleeping bad blocks. Thanks a lot for clarification. >> When can one need to run a "daily forced resync", and in which >> circumstances? > > As I said, I think the 'daily' is an error. What exactly do you have > in crontab?? Indeed, the crontab entry is wrong: # by default, run at 01:06 on the first Sunday of each month. 6 1 1-7 * 7 root [ -x /usr/share/mdadm/checkarray ] && /usr/share/mdadm/checkarray --cron --all --quiet However, it will run at 01:06, on 1st-7th day of each month, and on Sundays (Debian etch). -- Tomasz Chmielewski http://wpkg.org