[Gluster-users] General questions

Fri Jun 21 07:12:26 UTC 2019

Thanks Strahil,

in this link
https://access.redhat.com/documentation/en-us/red_hat_gluster_storage/3.4/html/administration_guide/sect-creating_replicated_volumes
i see:

*Sharding has one supported use case: in the context of providing Red Hat
Gluster Storage as a storage domain for Red Hat Enterprise Virtualization,
to provide storage for live virtual machine images. Note that sharding is
also a requirement for this use case, as it provides significant
performance improvements over previous implementations. *

The deafult setting in GusterFS 6.1 appears to be:

features.shard-block-size               64MB

features.shard-lru-limit                16384

features.shard-deletion-rate            100

Bricks in my case are over an xfs filesystem. I'll try different block-size
but if I understand correctly, small block sizes are preferable to big
block sizes and If i have doubt I will put 4M.

Very thanks for the warning, message received! :-)

Best Regards,

Cristian

Il giorno gio 20 giu 2019 alle ore 22:13 Strahil Nikolov <
hunter86_bg at yahoo.com> ha scritto:

> Sharding is complex. It helps to heal faster -as only the shards that got
> changed will be replicated, but imagine a 1GB shard that got only 512k
> updated - in such case you will copy the whole shard to the other replicas.
> RHV & oVirt use a default shard size of 4M which is the exact size of the
> default PE in LVM.
>
> On the other side, it speeds stuff as gluster can balance the shards
> properly on the replicas and thus you can evenly distribute the load on the
> cluster.
> It is not a coincidence that RHV and oVirt use sharding by default.
>
> Just a warning.
> NEVER, EVER, DISABLE SHARDING!!! ONCE ENABLED - STAYS ENABLED!
> Don't ask how I learnGrazie dell'avviso, messaggio ricevuto!t that :)
>
> Best Regards,
> Strahil Nikolov
>
>
>
> В четвъртък, 20 юни 2019 г., 18:32:00 ч. Гринуич+3, Cristian Del Carlo <
> cristian.delcarlo at targetsolutions.it> написа:
>
>
> Hi,
>
> thanks for your help.
>
> I am planing to use libvirtd with plain KVM.
>
> Ok i will use libgfapi.
>
> I'm confused about the use of sharding is it useful in this configuration?
> Doesn't sharding help limit the bandwidth in the event of a rebalancing?
>
> In the vm setting so i need to use directsync to avoid corruption.
>
> Thanks again,
>
> Il giorno gio 20 giu 2019 alle ore 12:25 Strahil <hunter86_bg at yahoo.com>
> ha scritto:
>
> Hi,
>
> Are you planing to use oVirt or plain KVM or openstack?
>
> I would recommend you to use gluster v6.1 as it is the latest stable
> version and will have longer support than the older versions.
>
> Fuse vs libgfapi - use the latter as it has better performance and less
> overhead on the host.oVirt does supports both libgfapi and fuse.
>
> Also, use replica 3 because you will have better read performance compared
> to replica 2 arbiter 1.
>
> Sharding is a tradeoff  between CPU (when there is no sharding , gluster
> shd must calculate the offset of the VM disk) and bandwidth (whole shard
> is being replicated despite even 512 need to be synced).
>
> If you will do live migration -  you do not want to cache in order to
> avoid  corruption.
> Thus oVirt is using direct I/O.
> Still, you can check the gluster settings mentioned in Red Hat
> documentation for Virt/openStack .
>
> Best Regards,
> Strahil Nikolov
> On Jun 20, 2019 13:12, Cristian Del Carlo <
> cristian.delcarlo at targetsolutions.it> wrote:
>
> Hi,
>
> I'm testing glusterfs before using it in production, it should be used to
> store vm for nodes with libvirtd.
>
> In production I will have 4 nodes connected with a dedicated 20gbit/s
> network.
>
> Which version to use in production on a centos 7.x? Should I use Gluster
> version 6?
>
> To make the volume available to libvirtd the best method is to use FUSE?
>
> I see that stripped is deprecated. Is it reasonable to use the volume with
> 3 replicas on 4 nodes and  sharding enabled?
> Is there convenience to use sharding volume in this context? I think could
> positive inpact in read performance or rebalance. Is it true?
>
> In the vm configuration I use the virtio disk. How is it better to set the
> disk cache to get the best performances none, default or writeback?
>
> Thanks in advance for your patience and answers.
>
> Thanks,
>
>
> *Cristian Del Carlo*
>
>
>
> --
>
>
> *Cristian Del Carlo*
>
> *Target Solutions s.r.l.*
>
> *T* +39 0583 1905621
> *F* +39 0583 1905675
> *@* cristian.delcarlo at targetsolutions.it
>
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