Hello all! This problem is solved by me today. Root of all in the incompatibility of gluster cache and kvm cache. Bug reproduces if KVM virtual machine created with cache=writethrough (default for OpenStack) option and hosted on GlusterFS volume. If any other (cache=writeback or cache=none with direct-io) cacher used, performance of writing to existing file inside VM is equal to bare storage (from host machine) write performance. I think, it must be documented in Gluster and maybe filled a bug. Other question. Where I can read something about gluster tuning (optimal cache size, write-behind, flush-behind use cases and other)? I found only options list, without any how-to or tested cases. 2013/3/5 Toby Corkindale <toby.corkindale at strategicdata.com.au> > On 01/03/13 21:12, Brian Candler wrote: > >> On Fri, Mar 01, 2013 at 03:30:07PM +0600, Nikita A Kardashin wrote: >> >>> If I try to execute above command inside virtual machine (KVM), first >>> time all going right - about 900MB/s (cache effect, I think), but if >>> I >>> run this test again on existing file - task (dd) hungs up and can be >>> stopped only by Ctrl+C. >>> Overall virtual system latency is poor too. For example, apt-get >>> upgrade upgrading system very, very slow, freezing on "Unpacking >>> replacement" and other io-related steps. >>> Does glusterfs have any tuning options, that can help me? >>> >> >> If you are finding that processes hang or freeze indefinitely, this is not >> a question of "tuning", this is simply "broken". >> >> Anyway, you're asking the wrong person - I'm currently in the process of >> stripping out glusterfs, although I remain interested in the project. >> >> I did find that KVM performed very poorly, but KVM was not my main >> application and that's not why I'm abandoning it. I'm stripping out >> glusterfs primarily because it's not supportable in my environment, >> because >> there is no documentation on how to analyse and recover from failure >> scenarios which can and do happen. This point in more detail: >> http://www.gluster.org/**pipermail/gluster-users/2013-** >> January/035118.html<http://www.gluster.org/pipermail/gluster-users/2013-January/035118.html> >> >> The other downside of gluster was its lack of flexibility, in particular >> the >> fact that there is no usage scaling factor on bricks, so that even with a >> simple distributed setup all your bricks have to be the same size. Also, >> the object store feature which I wanted to use, has clearly had hardly any >> testing (even the RPM packages don't install properly). >> >> I *really* wanted to deploy gluster, because in principle I like the idea >> of >> a virtual distribution/replication system which sits on top of existing >> local filesystems. But for storage, I need something where operational >> supportability is at the top of the pile. >> > > I have to agree; GlusterFS has been in use here in production for a while, > and while it mostly works, it's been fragile and documentation has been > disappointing. Despite 3.3 being in beta for a year, it still seems to have > been poorly tested. For eg, I can't believe almost no-one else noticed that > the log files were busted.. nor that the bug report has been around for > quarter of a year without being responded to or fixed. > > I have to ask -- what are you moving to now, Brian? > > -Toby > > > ______________________________**_________________ > Gluster-users mailing list > Gluster-users at gluster.org > http://supercolony.gluster.**org/mailman/listinfo/gluster-**users<http://supercolony.gluster.org/mailman/listinfo/gluster-users> > -- With best regards, differentlocal (www.differentlocal.ru | differentlocal at gmail.com), System administrator. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://supercolony.gluster.org/pipermail/gluster-users/attachments/20130305/b5b5f19d/attachment.html>
