From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: Linux Software RAID a bit of a weakness? Date: Fri, 23 Feb 2007 15:08:56 -0500 (EST) Message-ID: References: <1172258378.21648.51.camel@cowie> <45DF46B7.3040707@maine.edu> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: <45DF46B7.3040707@maine.edu> Sender: linux-raid-owner@vger.kernel.org To: Steve Cousins Cc: Colin Simpson , linux-raid@vger.kernel.org List-Id: linux-raid.ids This is the most useful thing I have found in a long time! p34:~# echo check > /sys/block/md0/md/sync_action $ cat /sys/block/md[0-4]/md/mismatch_cnt 512 0 0 0 0 Wow! Justin. On Fri, 23 Feb 2007, Steve Cousins wrote: > Colin Simpson wrote: >> Hi, >> We had a small server here that was configured with a RAID 1 mirror, >> using two IDE disks. >> Last week one of the drives failed in this. So we replaced the drive and >> set the array to rebuild. The "good" disk then found a bad block and the >> mirror failed. >> >> Now I presume that the "good" disk must have had an underlying bad block >> in either unallocated space or a file I never access. Now as RAID works >> at the block level you only ever see this on an array rebuild when it's >> often catastrophic. Is this a bit of a flaw? >> I know there is the definite probability of two drives failing within a >> short period of time. But this is a bit different as it's the >> probability of two drives failing but over a much larger time scale if >> one of the flaws is hidden in unallocated space (maybe a dirt particle >> finds it's way onto the surface or something). This would make RAID buy >> you a lot less in reliability, I'd have thought. >> I seem to remember seeing in the log file for a Dell perc something >> about scavenging for bad blocks. Do hardware RAID systems have a >> mechanism that at times of low activity search the disks for bad blocks >> to help guard against this sort of failure (so a disk error is reported >> early)? >> >> On Software RAID, I was thinking apart from a three way mirror, which I >> don't think is at present supported. Is there any merit in say, cat'ing >> the whole disk devices to /dev/null every so often to check that the >> whole surface is readable (I presume just reading the raw device won't >> upset thing, don't worry I don't plan on trying it on a production >> system). >> Any thoughts? As I presume people have thought of this before and I must >> be missing something. > > Yes, this is an important thing to keep on top of, both for hardware RAID and > software RAID. For md: > > echo check > /sys/block/md0/md/sync_action > > This should be done regularly. I have cron do it once a week. > > Check out: http://neil.brown.name/blog/20050727141521-002 > > Good luck, > > Steve > -- > ______________________________________________________________________ > Steve Cousins, Ocean Modeling Group Email: cousins@umit.maine.edu > Marine Sciences, 452 Aubert Hall http://rocky.umeoce.maine.edu > Univ. of Maine, Orono, ME 04469 Phone: (207) 581-4302 > > > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >