Recently, ZFS removed the pool global io stats from
/proc/spl/kstat/zfs/POOL/io with no replacement.
To gather stats about the datastores, access now the objset specific
entries there. To be able to make that efficient, cache a map of
dataset <-> obset ids, so that we do not have to parse all files each time.
We update the cache each time we try to get the info for a dataset
where we do not have a mapping.
We cannot update it on datastore add/remove since that happens in the
proxmox-backup daemon, while we need the info here in proxmox-backup-proxy.
Sadly with this we lose the io wait metric, but it seems that this is no
longer tracked in zfs at all, so nothing we can do for that.
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
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