abh1sar commented on PR #12758:
URL: https://github.com/apache/cloudstack/pull/12758#issuecomment-4023704310
Hi Joao,
This looks promising. Incremental backups, quick restore and file restore
features have been missing from CloudStack KVM.
I am having trouble understanding some of the design choices though:
1. What’s the reason behind strong coupling with secondary storage?
- I am wondering if the Backup Repository will provide a more flexible
alternative. The user would be free to add an external storage server or use
the secondary storage by simply adding it as a backup repository? It will be
very easy for user to have multiple backup repository attached to multiple
backup offerings which can be assigned to instance as required.
This will also be consistent with other backup providers like Veeam
and NAS which have the concept of backup repository.
The backup repository feature also comes with a separate capacity
tracking and email alerts.
- If a secondary storage is needed just for backup’s purpose, how will
it be ensured that templates and snapshots are not copied over to it?
2. About Qemu compression
- Have you measured / compared the performance of qemu-img compression
with other compression methods?
- As I understand, qemu-img compresses the qcow2 file at a cluster
granularity (usually 64kb). That might not fare well when compared to storage
level compression. In production environments, the operator might choose to
have compression at the storage layer if they are using an enterprise storage
like NetApp. Even something open source like ZFS might perform better than
qemu-img compress due to the granularity limitation that qemu compression has.
- I am making this point because the compression part is introducing a
fair bit of complexity due to the interaction with SSVM, and I am just
wondering if the gains are worth the trouble and should compression be
offloaded to the storage completely.
3. Do we need a separate backup offering table and api?
- Why not add column or details to backup_offering or
backup_offering_details? Other offerings can also benefit from these settings.
4. What’s the reason behind using virDomainSnapshotCreate to create backup
files and not virDomainBackupBegin like incremental volume snapshots and NAS
backup?
- Did you face any issues with checkpoints and bitmaps?
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