[DRBD-user] Regarding Best way for snapshotting with ZFS/LVM as backing disk for drbd

[Chitvan Chhabra]

Please suggest the Best Way to snapshot Secondary DRBD Volume(Upper) on
LVM/ZFS(Backing) using protocol A i.e Minor Data Loss(few Seconds) is OK
but data should remain crash consistent like Database.Also Metadata is
external in secondary. So Do i need to snapshot external metadata as well.
if yes Why ?


On Above few Queries are detailed below:


1)As per valuable suggestions by community that normal ZFS/LVM Snapshots
would do as long as it is upto date? How to know that in realtime uptodate
Status as drdbadm status command doesnot appear to be realtime in nature as
it takes time to reflect actual Status for example when primary goes down ,
only after few seconds only it shows as connecting


2) Community has again suggested for internal only metadata to have
simultaneous/atomic snapshot of both data and metadata .If the primary is
having external metadata , it makes sense to have external metadata in
secondary as well. But Why do we need to preserve the metadata via snapshot
at the first place as it is believed that once you rollback the using the
snapshot drbd would get confused and would attempt resynchronisation of the
entire device again any way


3) Do i need to suspend-io first before taking the snapshot and then check
up to date Status mandatorily ?


4) Last Query is regarding metadata, Does Metadata contains actual data in
the form of Activity log/extents.Then what is drbdadm apply-al is
for?Depending on the reply of this query we would be able to get crash
consistent data (via backing disk snapshot clone ofcourse) even if we loose
the metadata


Thanks and Regards,

Chitvan Chhabra

+919911208768
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