[Gluster-users] Brick Reboot => VMs slowdown, client crashes

Carl Sirotic csirotic at evoqarchitecture.com
Thu Aug 29 20:02:03 UTC 2019


this makes alot of sense.

It's the behavior that I was experiencing that makes no sense.

When one node was shut down, the whole VM cluster locked up.

However, I managed to find that the culprit were the quorum settings.

I put the quorum at 2 bricks for quorum now, and I am not experiencing 
the problem anymore.

All my vm boot disks and data disks are now sharded.

We are on 10gbit networks, when the node comes backs, we do not see any 
latency really.


On 2019-08-29 3:58 p.m., Darrell Budic wrote:
> You may be mis-understanding the way the gluster system works in 
> detail here, but you’ve got the right idea overall. Since gluster is 
> maintaining 3 copies of your data, you can lose a drive or a whole 
> system and things will keep going without interruption (well, mostly, 
> if a host node was using the system that just died, it may pause 
> briefly before re-connecting to one that is still running via a 
> backup-server setting or your dns configs). While the system is still 
> going with one node down, that node is falling behind and new disk 
> writes, and the remaining ones are keeping track of what’s changing. 
> Once you repair/recover/reboot the down node, it will rejoin the 
> cluster. Now the recovered system has to catch up, and it does this by 
> having the other two nodes send it the changes. In the meantime, 
> gluster is serving any reads for that data from one of the up to date 
> nodes, even if you ask the one you just restarted. In order to do this 
> healing, it had to lock the files to ensure no changes are made while 
> it copies a chunk of them over the recovered node. When it locks them, 
> your hypervisor notices they have gone read-only, and especially if it 
> has a pending write for that file, may pause the VM because this looks 
> like a storage issue to it. Once the file gets unlocked, it can be 
> written again, and your hypervisor notices and will generally 
> reactivate your VM. You may see delays too, especially if you only 
> have 1G networking between your host nodes while everything is getting 
> copied around. And your files could be being locked, updated, 
> unlocked, locked again a few seconds or minutes later, etc.
> That’s where sharding comes into play, once you have a file broken up 
> into shards, gluster can get away with only locking the particular 
> shard it needs to heal, and leaving the whole disk image unlocked. You 
> may still catch a brief pause if you try and write the specific 
> segment of the file gluster is healing at the moment, but it’s also 
> going to be much faster because it’s a small chuck of the file, and 
> copies quickly.
> Also, check out 
> https://staged-gluster-docs.readthedocs.io/en/release3.7.0beta1/Features/server-quorum/, 
> you probably want to set cluster.server-quorum-ratio to 50 for a 
> replica-3 setup to avoid the possibility of split-brains. Your cluster 
> will go write only if it loses two nodes though, but you can always 
> make a change to the server-quorum-ratio later if you need to keep it 
> running temporarily.
> Hope that makes sense of what’s going on for you,
>   -Darrell
>> On Aug 23, 2019, at 5:06 PM, Carl Sirotic 
>> <csirotic at evoqarchitecture.com 
>> <mailto:csirotic at evoqarchitecture.com>> wrote:
>> Okay,
>> so it means, at least I am not getting the expected behavior and 
>> there is hope.
>> I put the quorum settings that I was told a couple of emails ago.
>> After applying virt group, they are
>> cluster.quorum-type auto
>> cluster.quorum-count (null)
>> cluster.server-quorum-type server
>> cluster.server-quorum-ratio 0
>> cluster.quorum-reads no
>> Also,
>> I just put the ping timeout to 5 seconds now.
>> Carl
>> On 2019-08-23 5:45 p.m., Ingo Fischer wrote:
>>> Hi Carl,
>>> In my understanding and experience (I have a replica 3 System 
>>> running too) this should not happen. Can you tell your client and 
>>> server quorum settings?
>>> Ingo
>>> Am 23.08.2019 um 15:53 schrieb Carl Sirotic 
>>> <csirotic at evoqarchitecture.com <mailto:csirotic at evoqarchitecture.com>>:
>>>> However,
>>>> I must have misunderstood the whole concept of gluster.
>>>> In a replica 3, for me, it's completely unacceptable, regardless of 
>>>> the options, that all my VMs go down when I reboot one node.
>>>> The whole purpose of having a full 3 copy of my data on the fly is 
>>>> suposed to be this.
>>>> I am in the process of sharding every file.
>>>> But even if the healing time would be longer, I would still expect 
>>>> a non-sharded replica 3 brick with vm boot disk, to not go down if 
>>>> I reboot one of its copy.
>>>> I am not very impressed by gluster so far.
>>>> Carl
>>>> On 2019-08-19 4:15 p.m., Darrell Budic wrote:
>>>>> /var/lib/glusterd/groups/virt is a good start for ideas, notably 
>>>>> some thread settings and choose-local=off to improve read 
>>>>> performance. If you don’t have at least 10 cores on your servers, 
>>>>> you may want to lower the recommended shd-max-threads=8 to no more 
>>>>> than half your CPU cores to keep healing from swamping out regular 
>>>>> work.
>>>>> It’s also starting to depend on what your backing store and 
>>>>> networking setup are, so you’re going to want to test changes and 
>>>>> find what works best for your setup.
>>>>> In addition to the virt group settings, I use these on most of my 
>>>>> volumes, SSD or HDD backed, with the default 64M shard size:
>>>>> performance.io <http://performance.io/>-thread-count: 32# seemed 
>>>>> good for my system, particularly a ZFS backed volume with lots of 
>>>>> spindles
>>>>> client.event-threads: 8
>>>>> cluster.data-self-heal-algorithm: full# 10G networking, uses more 
>>>>> net/less cpu to heal. probably don’t use this for 1G networking?
>>>>> performance.stat-prefetch: on
>>>>> cluster.read-hash-mode: 3# distribute reads to least loaded server 
>>>>> (by read queue depth)
>>>>> and these two only on my HDD backed volume:
>>>>> performance.cache-size: 1G
>>>>> performance.write-behind-window-size: 64MB
>>>>> but I suspect these two need another round or six of tuning to 
>>>>> tell if they are making a difference.
>>>>> I use the throughput-performance tuned profile on my servers, so 
>>>>> you should be in good shape there.
>>>>>> On Aug 19, 2019, at 12:22 PM, Guy Boisvert 
>>>>>> <guy.boisvert at ingtegration.com 
>>>>>> <mailto:guy.boisvert at ingtegration.com>> wrote:
>>>>>> On 2019-08-19 12:08 p.m., Darrell Budic wrote:
>>>>>>> You also need to make sure your volume is setup properly for 
>>>>>>> best performance. Did you apply the gluster virt group to your 
>>>>>>> volumes, or at least features.shard = on on your VM volume?
>>>>>> That's what we did here:
>>>>>> gluster volume set W2K16_Rhenium cluster.quorum-type auto
>>>>>> gluster volume set W2K16_Rhenium network.ping-timeout 10
>>>>>> gluster volume set W2K16_Rhenium auth.allow \*
>>>>>> gluster volume set W2K16_Rhenium group virt
>>>>>> gluster volume set W2K16_Rhenium storage.owner-uid 36
>>>>>> gluster volume set W2K16_Rhenium storage.owner-gid 36
>>>>>> gluster volume set W2K16_Rhenium features.shard on
>>>>>> gluster volume set W2K16_Rhenium features.shard-block-size 256MB
>>>>>> gluster volume set W2K16_Rhenium cluster.data-self-heal-algorithm 
>>>>>> full
>>>>>> gluster volume set W2K16_Rhenium performance.low-prio-threads 32
>>>>>> tuned-adm profile random-io (a profile i added in CentOS 7)
>>>>>> cat /usr/lib/tuned/random-io/tuned.conf
>>>>>> ===========================================
>>>>>> [main]
>>>>>> summary=Optimize for Gluster virtual machine storage
>>>>>> include=throughput-performance
>>>>>> [sysctl]
>>>>>> vm.dirty_ratio = 5
>>>>>> vm.dirty_background_ratio = 2
>>>>>> Any more optimization to add to this?
>>>>>> Guy
>>>>>> -- 
>>>>>> Guy Boisvert, ing.
>>>>>> IngTegration inc.
>>>>>> http://www.ingtegration.com <http://www.ingtegration.com/>
>>>>>> https://www.linkedin.com/in/guy-boisvert-8990487
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