From mboxrd@z Thu Jan 1 00:00:00 1970 From: Goswin von Brederlow Subject: Re: RAID5 / 6 Growth Date: Fri, 18 Dec 2009 13:27:05 +0100 Message-ID: <87hbroqxgm.fsf@frosties.localdomain> References: <1C.0E.01567.69E892B4@cdptpa-omtalb.mail.rr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: In-Reply-To: <1C.0E.01567.69E892B4@cdptpa-omtalb.mail.rr.com> (Leslie Rhorer's message of "Wed, 16 Dec 2009 19:51:18 -0600") Sender: linux-raid-owner@vger.kernel.org To: Leslie Rhorer Cc: goswin-v-b@web.de, linux-raid@vger.kernel.org List-Id: linux-raid.ids "Leslie Rhorer" writes: >> > High enough? Wouldn't a higher speed limit mean more stress on the >> systems? >> > Its value is 1000. >> >> A higher min value will block more normal IO (if there is >> any). > > No, not really. All the system that is currently being grown does > is incrementally rsync the data from the main server every morning. The > main server, which will be grown after this server is done, is another > matter. > >> Raising min is usefull to ensure the job gets done in a certain >> time, to not let normal IO slow down a rebuild too much. > > OK, but like I said, for the most part there isn't any other I/O. > >> >> MB/s) along with /proc/sys/dev/raid/speed_limit_max? >> > >> > It's 200,000 >> >> I only ever had to tune this once when too much IO would deadlock an >> external enclosure. Otherwise keep this really high so it uses all >> idle IO there is. > > 200MBps is far more than the system can handle. These are consumer > class drives on a relatively inexpensive 4 port controller feeding a Port > Multiplier chassis. > >> As to your initial question: Being able to keep the filesystem mounted >> and used is the whole point of having online growing of the raid >> system. If that weren't save then there would be no point to it as you >> could just as well stop the raid if you already umounted it and grow >> it offline. > > I know that is the point of the utility. My question boils down to, > "How safe is it to avail one's self of the capability if it is not essential > to have the array mounted for the duration?" I don't particularly like > having the array unavailable (especially not for nearly 5 days), but I > prefer that to risking data loss, or especially risking irretrievably losing > the entire array. The question is particularly pertinent given the fact the > growth is going to take nearly 5 days (a lot can happen in 5 days), and the > fact the system was having the rather squirrelly issue a few days back which > seems - emphasis on SEEMS - to have been resolved by disabling NCQ. What > happens if the system kicks a couple of drives, especially if one drive gets > kicked, a bunch of data gets written and then a few minutes later another > drive gets kicked? In particular, what if neither of the two drives that > get kicked are the new drive? It should just keep going. I don't see how having the filesystem in use will have any influence there other than adding a little more load on the disks. Reshaping is heavy on the drive. Lots of reads, writes and seeks. A daily rsync probably doesn't even register as extra load. MfG Goswin