> Message: 12 > Date: Fri, 29 May 2015 16:29:37 +0100 > From: Joe Thornber <thornber@xxxxxxxxxx> > To: device-mapper development <dm-devel@xxxxxxxxxx> > Subject: Re: Poor snapshot performance in linux-3.19 > Message-ID: <20150529152936.GA4297@rh-vpn> > Content-Type: text/plain; charset=us-ascii > > On Fri, May 29, 2015 at 11:03:28AM +0800, Dennis Yang wrote: >> The server I have tested is equipped with Xeon E3-1246 with 4 physical >> cores, so I think CPU might not be the bottleneck of the storage >> throughput. >> Any idea? > > Is it any better with this patch? > > https://github.com/jthornber/linux-2.6/commit/56db3d227ea7e11e42b2b67f8ddc9f6d40c3a3a4 > Hi, I just gave it a try this morning, but it looks like the performance is still the same (drop from 1.8GB/s to 270MB/s after snapshot). I also make some other experiments. If I make a EXT4 filesystem on top of a thin device with 64K pool block size, the file I/O throughput after snapshot is great (drop from 1.2GB/s to 1GB/s only) because of the bio size is 64KB equals to the pool block size. This makes me start wondering what throughput level we should expect after snapshotted. Since we are making 1 write to (1 read + 1 write) + 1 write to complete a write request, maybe the best performance we can get here is around 25~30% of throughput before snapshot. Please correct me if I get anything wrong. Thanks, Dennis -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
