From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Cody Yellan" Subject: Re: raid5 grow reshaping speed is unchangeable Date: Fri, 28 Dec 2007 11:21:39 -0800 Message-ID: <380-2200712528192139967@mochamail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids >>> Cody Yellan wrote: >>>> I had a 4x500GB SATA2 array, md0. I added one 500GB drive and >>>> reshaping began at ~2500K/sec. Changing >>>> /proc/sys/dev/raid/speed_limit_m{in,ax} or >>>> /sys/block/md0/md/sync_speed_m{in,ax} had no effect. I shut down >all >>>> unnecessary services and the array is offline (not mounted). I >have >>>> read that the throttling code is "fragile" (esp. with regard to >>>> raid5) but does this make sense? I will wait (in)patiently for >it to >>>> finish, but I do wonder why the configuration parameters have no >>>> effect. This is a dual quad 2GHz Xeon machine with 8GB of memory >>>> running RHEL5. Is this the maximum speed? >> >>Are you running a non-standard /sys/block/md5/md/stripe_cache_size? >> >>I found when running a kernel of about that vintage on FC6 (which I >>guess became RHEL5), that with a stripe_cache_size of 16384, resyncs > >>dropped down to about the speed you are seeing. >> >>This changed back to more normal speeds with a later kernel, but I >do >>not recall which. >> >>Regards, >> >>Richard You are right, Richard. RHEL5 had a stripe_cache_size of 256 when the reshape began. I increased it to 1024 and the reshape speed doubled to 4500K/s. I did not see any increase in memory usage. I tried 2048 and then 4096 but saw no difference in speed. The reshape finished and the array is back online. mdadm works very well, but I would like to better understand how it works. For instance, the mdadm man page says a backup-file is necessary to grow a RAID5, but this does not appear necessary now. Anyway, it's a wonderful tool.