[ovirt-users] Re: What if anything can be done to improve small file performance with gluster?

No worries at all about the length of the email, the details are highly appreciated. You've given me lots to look into and consider. On Sat, Mar 7, 2020 at 10:02 AM Strahil Nikolov <hunter86_bg(a)yahoo.com&gt; wrote: > On March 7, 2020 1:12:58 PM GMT+02:00, Jayme <jaymef(a)gmail.com&gt; wrote: > >Thanks again for the info. You’re probably right about the testing > >method. > >Though the reason I’m down this path in the first place is because I’m > >seeing a problem in real world work loads. Many of my vms are used in > >development environments where working with small files is common such > >as > >npm installs working with large node_module folders, ci/cd doing lots > >of > >mixed operations io and compute. > > > >I started testing some of these things by comparing side to side with a > >vm > >using same specs only difference being gluster vs nfs storage. Nfs > >backed > >storage is performing about 3x better real world. > > > >Gluster version is stock that comes with 4.3.7. I haven’t attempted > >updating it outside of official ovirt updates. > > > >I’d like to see if I could improve it to handle my workloads better. I > >also > >understand that replication adds overhead. > > > >I do wonder how much difference in performance there would be with > >replica > >3 vs replica 3 arbiter. I’d assume arbiter setup would be faster but > >perhaps not by a considerable difference. > > > >I will check into c states as well > > > >On Sat, Mar 7, 2020 at 2:52 AM Strahil Nikolov <hunter86_bg(a)yahoo.com&gt; > >wrote: > > > >> On March 7, 2020 1:09:37 AM GMT+02:00, Jayme <jaymef(a)gmail.com&gt; > >wrote: > >> >Strahil, > >> > > >> >Thanks for your suggestions. The config is pretty standard HCI setup > >> >with > >> >cockpit and hosts are oVirt node. XFS was handled by the deployment > >> >automatically. The gluster volumes were optimized for virt store. > >> > > >> >I tried noop on the SSDs, that made zero difference in the tests I > >was > >> >running above. I took a look at the random-io-profile and it looks > >like > >> >it > >> >really only sets vm.dirty_background_ratio = 2 & vm.dirty_ratio = 5 > >-- > >> >my > >> >hosts already appear to have those sysctl values, and by default are > >> >using virtual-host tuned profile. > >> > > >> >I'm curious what a test like "dd if=/dev/zero of=test2.img bs=512 > >> >count=1000 oflag=dsync" on one of your VMs would show for results? > >> > > >> >I haven't done much with gluster profiling but will take a look and > >see > >> >if > >> >I can make sense of it. Otherwise, the setup is pretty stock oVirt > >HCI > >> >deployment with SSD backed storage and 10Gbe storage network. I'm > >not > >> >coming anywhere close to maxing network throughput. > >> > > >> >The NFS export I was testing was an export from a local server > >> >exporting a > >> >single SSD (same type as in the oVirt hosts). > >> > > >> >I might end up switching storage to NFS and ditching gluster if > >> >performance > >> >is really this much better... > >> > > >> > > >> >On Fri, Mar 6, 2020 at 5:06 PM Strahil Nikolov > &gt;&lt;hunter86_bg(a)yahoo.com&gt; > >> >wrote: > >> > > >> >> On March 6, 2020 6:02:03 PM GMT+02:00, Jayme <jaymef(a)gmail.com&gt; > >> >wrote: > >> >> >I have 3 server HCI with Gluster replica 3 storage (10GBe and SSD > >> >> >disks). > >> >> >Small file performance inner-vm is pretty terrible compared to a > >> >> >similar > >> >> >spec'ed VM using NFS mount (10GBe network, SSD disk) > >> >> > > >> >> >VM with gluster storage: > >> >> > > >> >> ># dd if=/dev/zero of=test2.img bs=512 count=1000 oflag=dsync > >> >> >1000+0 records in > >> >> >1000+0 records out > >> >> >512000 bytes (512 kB) copied, 53.9616 s, 9.5 kB/s > >> >> > > >> >> >VM with NFS: > >> >> > > >> >> ># dd if=/dev/zero of=test2.img bs=512 count=1000 oflag=dsync > >> >> >1000+0 records in > >> >> >1000+0 records out > >> >> >512000 bytes (512 kB) copied, 2.20059 s, 233 kB/s > >> >> > > >> >> >This is a very big difference, 2 seconds to copy 1000 files on > >NFS > >> >VM > >> >> >VS 53 > >> >> >seconds on the other. > >> >> > > >> >> >Aside from enabling libgfapi is there anything I can tune on the > >> >> >gluster or > >> >> >VM side to improve small file performance? I have seen some > >guides > >> >by > >> >> >Redhat in regards to small file performance but I'm not sure > >what/if > >> >> >any of > >> >> >it applies to oVirt's implementation of gluster in HCI. > >> >> > >> >> You can use the rhgs-random-io tuned profile from > >> >> > >> > > >> > > > ftp://ftp.redhat.com/redhat/linux/enterprise/7Server/en/RHS/SRPMS/redhat-... > >> >> and try with that on your hosts. > >> >> In my case, I have modified it so it's a mixture between > >> >rhgs-random-io > >> >> and the profile for Virtualization Host. > >> >> > >> >> Also,ensure that your bricks are using XFS with relatime/noatime > >> >mount > >> >> option and your scheduler for the SSDs is either 'noop' or 'none' > >> >.The > >> >> default I/O scheduler for RHEL7 is deadline which is giving > >> >preference to > >> >> reads and your workload is definitely 'write'. > >> >> > >> >> Ensure that the virt settings are enabled for your gluster > >volumes: > >> >> 'gluster volume set <volname> group virt' > >> >> > >> >> Also, are you running on fully allocated disks for the VM or you > >> >started > >> >> thin ? > >> >> I'm asking as creation of new shards at gluster level is a slow > >> >task. > >> >> > >> >> Have you checked gluster profiling the volume? It can clarify > >what > >> >is > >> >> going on. > >> >> > >> >> > >> >> Also are you comparing apples to apples ? > >> >> For example, 1 ssd mounted and exported as NFS and a replica 3 > >> >volume > >> >> of the same type of ssd ? If not, the NFS can have more iops due > >to > >> >> multiple disks behind it, while Gluster has to write the same > >thing > >> >on all > >> >> nodes. > >> >> > >> >> Best Regards, > >> >> Strahil Nikolov > >> >> > >> >> > >> > >> Hi Jayme, > >> > >> > >> My test are not quite good ,as I have a different setup: > >> > >> NVME - VDO - 4 thin LVs -XFS - 4 Gluster volumes (replica 2 arbiter > >1) > >> - 4 storage domains - striped LV in each VM > >> > >> RHEL7 VM (fully stock): > >> [root@node1 ~]# dd if=/dev/zero of=test2.img bs=512 count=1000 > >oflag=dsync > >> 1000+0 records in > >> 1000+0 records out > >> 512000 bytes (512 kB) copied, 19.8195 s, 25.8 kB/s > >> [root@node1 ~]# > >> > >> Brick: > >> [root@ovirt1 data_fast]# dd if=/dev/zero of=test2.img bs=512 > >count=1000 > >> oflag=dsync > >> 1000+0 records in > >> 1000+0 records out > >> 512000 bytes (512 kB) copied, 1.41192 s, 363 kB/s > >> > >> As I use VDO with compression (on 1/4 of the NVMe) - I cannot expect > >any > >> performance from it. > >> > >> > >> Is your app really using dsync ? I have seen many times that > >performance > >> testing with the wrong tools/tests cause more trouble than it > >should. > >> > >> I would recommend you to test with a real workload before deciding to > >> change the architecture. > >> > >> I forgot to mention that you need to disable c states for your > >systems if > >> you are chasing performance. > >> Run a gluster profile while you run real workload in your VMs and > >then > >> provide that for analysis. > >> > >> Which version of Gluster are you using ? > >> > >> Best Regards, > >> Strahil Nikolov > >> > > Hm... > Then you do have a real workload scenario - pick one of the most often > used tasks and use it's time of completion for reference. > Synthetic benchmarking is not good. > > As far as I know oVirt is actually running on gluster v6.X . > @Sandro, > Can you hint us the highest supported gluster version on oVirt ? I'm > running v7.0, so I'm little bit off the track. > > Jayme, > > Next steps are to check: > 1. Did you disable cstates - there are very good articles for > RHEL/CentOS 7 > 2. Check firmware of your HCI nodes - I've seen numerous network/SAN > issues due to old firmware including stucked processes > 3. Check the articles for RHV and hugepages . If your VMs are memory > dynamic and lots of RAM is needed -> hugepages will bring more performance. > Second , transparent huge pages must be disabled. > 4. Create a High Performance VM for testing purposes with fully > allocated disks > 5. Check if 'noatime' or 'relatime' is set for the bricks. If selinux > is in enforcing mode (I highly recommend that), you can use mount option > 'system_u:object_r:glusterd_brick_t:s0' which will cause the kernel to > reduce lookups to check the SELINUX context of all files in the brick - > and increasing the performance. > > 6. Consider switching to 'noop'/'none' or tuning 'deadline' I/O scheduler > to match your needs > > 7. Create a gluster profile during the VM(step 4) is being tested , as > if is needed. > > 8. Consider using 'Pass-through host cpu' which is enabled in UI via > -> VM-> edit -> Host -> Start on specific host -> select all hosts with > the same cpu -> allow manual and automatic migration -> OK > This mode allows all instructions on the Host CPU to be available on > the guest, greatly increasing performance for a lot of software. > > > The difference between 'replica 3' and 'replica 3 arbiter 1' (old name > was 'replica 2 arbiter 1' but it means the same) is the fact that the > arbitrated volume requiress less bandwidth (due to the fact that the > files on the arbiter has 0 bytes of data) and stores only metadata to > prevent splitbrain. > Drawbacks of the arbiter is that you have only 2 sources to read from, > while replica 3 provides three sources to read from. > With glusterd 2.0 ( I think it was introduced in gluster v7 ) the arbiter > doesn't need to be locally (which means higher lattencies are no longer an > issue), and is only needed when one of data bricks is needed.Still, the > remote arbiter is too new for prod. > > Next: You can consider clusterized 2-node NFS Ganesha (with quorum > device for the third vote) as an NFS source. The good thing about NFS > Ganes is the primary focus from the Gluster community and it uses > libgfapi to connect to the backend (replica volume). > > I think it's enough for now , but I guess other stuff could come to > my mind at later stage. > > Edit: This e-mail is way longer than I initially thought to be.Sorry > about that. > > > Best Regards, > Strahil Nikolov >