From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@horizon.com Subject: Re: scrub was Re: RAID5 Problem - $1000 reward for help Date: 21 Sep 2006 16:20:08 -0400 Message-ID: <20060921202008.4872.qmail@science.horizon.com> Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids >> Does this test stress the discs a lot, like a resync? >> How long does it take? >> Can I use it on a mounted array? > I'd like to add to this question -- does 'check' action on a RAID5 array > verify the accuracy of parity data, blindly read back all data, or only > verify readability of data blocks? The former: it reads all data and verifies the parity. It's a bit hard to see buried in drivers/md/raid5.c:handle_stripe5(), which is more than a little intricate. If you search for MD_RECOVERY_CHECK in there, you can see where it rewrites the newly added disk if syncing or just notes the problem if checking.