Re: Backups

[Alvin Starr <alvin@xxxxxxxxxx>]

For volume backups you need something like snapshots.

If you take a snapshot A of a live volume L that snapshot stays at that moment in time and you can rsync that to another system or use something like deltacp.pl to copy it.

The usual process is to delete the snapshot once its copied and than repeat the process again when the next backup is required.

That process does require rsync/deltacp to read the complete volume on both systems which can take a long time.

I was kicking around the idea to try and handle snapshot deltas better.

The idea is that you could take your initial snapshot A then sync that snapshot to your backup system.

At a later point you could take another snapshot B.

Because snapshots contain the copies of the original data at the time of the snapshot and unmodified data points to the Live volume it is possible to tell what blocks of data have changed since the snapshot was taken.

Now that you have a second snapshot you can in essence perform a diff on the A and B snapshots to get only the blocks that changed up to the time that B was taken.

These blocks could be copied to the backup image and you should have a clone of the B snapshot.

You would not have to read the whole volume image but just the changed blocks dramatically improving the speed of the backup.

At this point you can delete the A snapshot and promote the B snapshot to be the A snapshot for the next backup round.

On 03/23/2017 03:53 PM, Gandalf Corvotempesta wrote:

Are backup consistent?

What happens if the header on shard0 is synced referring to some data on shard450 and when rsync parse shard450 this data is changed by subsequent writes?

Header would be backupped  of sync respect the rest of the image

Il 23 mar 2017 8:48 PM, "Joe Julian" <joe@xxxxxxxxxxxxxxxx> ha scritto:

The rsync protocol only passes blocks that have actually changed. Raw changes fewer bits. You're right, though, that it still has to check the entire file for those changes.

On 03/23/17 12:47, Gandalf Corvotempesta wrote:

Raw or qcow doesn't change anything about the backup.

Georep always have to sync the whole file

Additionally, raw images has much less features than qcow

Il 23 mar 2017 8:40 PM, "Joe Julian" <joe@xxxxxxxxxxxxxxxx> ha scritto:

I always use raw images. And yes, sharding would also be good.

On 03/23/17 12:36, Gandalf Corvotempesta wrote:

Georep expose to another problem:

When using gluster as storage for VM, the VM file is saved as qcow. Changes are inside the qcow, thus rsync has to sync the whole file every time

A little workaround would be sharding, as rsync has to sync only the changed shards, but I don't think this is a good solution

Il 23 mar 2017 8:33 PM, "Joe Julian" <joe@xxxxxxxxxxxxxxxx> ha scritto:

In many cases, a full backup set is just not feasible. Georep to the same or different DC may be an option if the bandwidth can keep up with the change set. If not, maybe breaking the data up into smaller more manageable volumes where you only keep a smaller set of critical data and just back that up. Perhaps an object store (swift?) might handle fault tolerance distribution better for some workloads.

There's no one right answer.

On 03/23/17 12:23, Gandalf Corvotempesta wrote:

Backing up from inside each VM doesn't solve the problem

If you have to backup 500VMs you just need more than 1 day and what if you have to restore the whole gluster storage?

How many days do you need to restore 1PB?

Probably the only solution should be a georep in the same datacenter/rack with a similiar cluster, 

ready to became the master storage.

In this case you don't need to restore anything as data are already there, 

only a little bit back in time but this double the TCO

Il 23 mar 2017 6:39 PM, "Serkan Çoban" <cobanserkan@xxxxxxxxx> ha scritto:

Assuming a backup window of 12 hours, you need to send data at 25GB/s
to backup solution.
Using 10G Ethernet on hosts you need at least 25 host to handle 25GB/s.
You can create an EC gluster cluster that can handle this rates, or
you just backup valuable data from inside VMs using open source backup
tools like borg,attic,restic , etc...

On Thu, Mar 23, 2017 at 7:48 PM, Gandalf Corvotempesta
<gandalf.corvotempesta@gmail.com> wrote:
> Let's assume a 1PB storage full of VMs images with each brick over ZFS,
> replica 3, sharding enabled
>
> How do you backup/restore that amount of data?
>
> Backing up daily is impossible, you'll never finish the backup that the
> following one is starting (in other words, you need more than 24 hours)
>
> Restoring is even worse. You need more than 24 hours with the whole cluster
> down
>
> You can't rely on ZFS snapshot due to sharding (the snapshot took from one
> node is useless without all other node related at the same shard) and you
> still have the same restore speed
>
> How do you backup this?
>
> Even georep isn't enough, if you have to restore the whole storage in case
> of disaster
>
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Alvin Starr                   ||   voice: (905)513-7688
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