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That really isnt an arbiter issue or for that matter a Gluster issue. We have seen that with vanilla NAS servers that had some issue or another. Arbiter simply makes it less likely to be an issue than replica 2 but in turn arbiter is less 'safe' than replica 3. However, in regards to Gluster and RO behaviour The default timeout for most OS versions is 30 seconds and the
Gluster timeout is 42, so yes you can trigger an RO event.
# cat /sys/block/sda/device/timeout # echo 90 > /sys/block/sda/device/timeout As a purely observational note, we have noticed that EXT3/4 filesystems on VMs will go read-only much easier than XFS systems (even with the default timeout and irregardless of storage type). We have always wondered about that, though part of that observation is biased because we tend to use XFS on newer VMs which mean newer, better kernels. Likewise virtio "disks" don't even have a timeout value that I am aware of and I don't recall them being extremely sensitive to disk issues on either Gluster, NFS or DAS. All our newer VMs use virtio instead of sata/ide emulation AND XFS so we rarely see a RO situation and if we do, it was a good thing the VMs did go RO to protect themselves while the storage system freaked out. On 8/23/2017 12:26 PM,
lemonnierk@xxxxxxxxx wrote:
Really ? I can't see why. But I've never used arbiter so you probably know more about this than I do. In any case, with replica 3, never had a problem. On Wed, Aug 23, 2017 at 09:13:28PM +0200, Pavel Szalbot wrote:Hi, I believe it is not that simple. Even replica 2 + arbiter volume with default network.ping-timeout will cause the underlying VM to remount filesystem as read-only (device error will occur) unless you tune mount options in VM's fstab. -ps On Wed, Aug 23, 2017 at 6:59 PM, <lemonnierk@xxxxxxxxx> wrote:What he is saying is that, on a two node volume, upgrading a node will cause the volume to go down. That's nothing weird, you really should use 3 nodes. On Wed, Aug 23, 2017 at 06:51:55PM +0200, Gionatan Danti wrote:Il 23-08-2017 18:14 Pavel Szalbot ha scritto:Hi, after many VM crashes during upgrades of Gluster, losing network connectivity on one node etc. I would advise running replica 2 with arbiter.Hi Pavel, this is bad news :( So, in your case at least, Gluster was not stable? Something as simple as an update would let it crash?I once even managed to break this setup (with arbiter) due to network partitioning - one data node never healed and I had to restore from backups (it was easier and kind of non-production). Be extremely careful and plan for failure.I would use VM locking via sanlock or virtlock, so a split brain should not cause simultaneous changes on both replicas. I am more concerned about volume heal time: what will happen if the standby node crashes/reboots? Will *all* data be re-synced from the master, or only changed bit will be re-synced? As stated above, I would like to avoid using sharding... Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@xxxxxxxxxx - info@xxxxxxxxxx GPG public key ID: FF5F32A8 _______________________________________________ Gluster-users mailing list Gluster-users@xxxxxxxxxxx http://lists.gluster.org/mailman/listinfo/gluster-users_______________________________________________ Gluster-users mailing list Gluster-users@xxxxxxxxxxx http://lists.gluster.org/mailman/listinfo/gluster-users |
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