[ovirt-users] Re: Gluster VM image Resync Time

Gluster 5.x does have two important performance-related fixes that are not part of 3.12.x - i. in shard-replicate interaction - https://bugzilla.redhat.com/show_bug.cgi?id=1635972

https://bugzilla.redhat.com/show_bug.cgi?id=1635980 The two fixes do improve write performance in vm-storage workload. Do let us know your experience if you happen to move to gluster-5.x. -Krutika On Thu, Mar 28, 2019 at 1:13 PM Strahil <hunter86_bg(a)yahoo.com&gt; wrote: > Hi Krutika, > > I have noticed some performance penalties (10%-15%) when using sharing > in v3.12 . > What is the situation now with 5.5 ? > Best Regards, > Strahil Nikolov > On Mar 28, 2019 08:56, Krutika Dhananjay <kdhananj(a)redhat.com&gt; wrote: > > Right. So Gluster stores what are called "indices" for each modified file > (or shard) > under a special hidden directory of the "good" bricks at > $BRICK_PATH/.glusterfs/indices/xattrop. > When the offline brick comes back up, the file corresponding to each > index is healed, and then the index deleted > to mark the fact that the file has been healed. > > You can try this and see it for yourself. Just create a 1x3 plain > replicate volume, and enable shard on it. > Create a big file (big enough to have multiple shards). Check that the > shards are created under $BRICK_PATH/.shard. > Now kill a brick. Modify a small portion of the file. Hit `ls` on > $BRICK_PATH/.glusterfs/indices/xattrop of the online bricks. > You'll notice there will be entries named after the gfid (unique > identifier in gluster for each file) of the shards. > And only for those shards that the write modified, and not ALL shards of > this really big file. > And then when you bring the brick back up using `gluster volume start > $VOL force`, the > shards get healed and the directory eventually becomes empty. > > -Krutika > > > On Thu, Mar 28, 2019 at 12:14 PM Indivar Nair <indivar.nair(a)techterra.in&gt; > wrote: > > Hi Krutika, > > So how does the Gluster node know which shards were modified after it > went down? > Do the other Gluster nodes keep track of it? > > Regards, > > > Indivar Nair > > > On Thu, Mar 28, 2019 at 9:45 AM Krutika Dhananjay <kdhananj(a)redhat.com&gt; > wrote: > > Each shard is a separate file of size equal to value of > "features.shard-block-size". > So when a brick/node was down, only those shards belonging to the VM that > were modified will be sync'd later when the brick's back up. > Does that answer your question? > > -Krutika > > On Wed, Mar 27, 2019 at 7:48 PM Sahina Bose <sabose(a)redhat.com&gt; wrote: > > On Wed, Mar 27, 2019 at 7:40 PM Indivar Nair <indivar.nair(a)techterra.in&gt; > wrote: > > > > Hi Strahil, > > > > Ok. Looks like sharding should make the resyncs faster. > > > > I searched for more info on it, but couldn't find much. > > I believe it will still have to compare each shard to determine whether > there are any changes that need to be replicated. > > Am I right? > > +Krutika Dhananjay > > > > Regards, > > > > Indivar Nair > > > > > > > > On Wed, Mar 27, 2019 at 4:34 PM Strahil <hunter86_bg(a)yahoo.com&gt; wrote: > >> > >> By default ovirt uses 'sharding' which splits the files into logical > chunks. This greatly reduces healing time, as VM's disk is not always > completely overwritten and only the shards that are different will be > healed. > >> > >> Maybe you should change the default shard size. > >> > >> Best Regards, > >> Strahil Nikolov > >> > >> On Mar 27, 2019 08:24, Indivar Nair <indivar.nair(a)techterra.in&gt; wrote: > >> > >> Hi All, > >> > >> We are planning a 2 + 1 arbitrated mirrored Gluster setup. > >> We would have around 50 - 60 VMs, with an average 500GB disk size. > >> > >> Now in case one of the Gluster Nodes go completely out of sync, > roughly, how long would it take to resync? (as per your experience) > >> Will it impact the working of VMs in any way? > >> Is there anything to be taken care of, in advance, to prepare for such > a situation? > >> > >> Regards, > >> > >> > >> Indivar Nair > >> > > ______________ > >