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 < [email protected]> 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 < > [email protected]> 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 <[email protected]> > 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 < > [email protected]> 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 > *@* [email protected] > > http://www.targetsolutions.it > P.IVA e C.Fiscale: 01815270465 Reg. Imp. di Lucca > Capitale Sociale: €11.000,00 iv - REA n° 173227 > > Il testo e gli eventuali documenti trasmessi contengono informazioni > riservate al destinatario indicato. La seguente e-mail e' confidenziale e > la sua riservatezza e' tutelata legalmente dal Decreto Legislativo 196 del > 30/06/2003 (Codice di tutela della privacy). La lettura, copia o altro uso > non autorizzato o qualsiasi altra azione derivante dalla conoscenza di > queste informazioni sono rigorosamente vietate. Qualora abbiate ricevuto > questo documento per errore siete cortesemente pregati di darne immediata > comunicazione al mittente e di provvedere, immediatamente, alla sua > distruzione. >
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