Using snapshots for backups on MD3000i?

Question

I'm having a bit of trouble trying to figure out how to do this. So, let me start by explaining what I want to do.

I have a md3000i w/ 2TB of SAS storage and 2TB of SATA. I'd like to attach a couple of servers running Virtual Server to a couple of virtual disks on the SAS side of the storage. I'd then like to be able to use the SATA side of the SAN for backups. Once it's on the other side, I could use something like Microsoft Data Protection Manager to back it up.

Problem is, I'm having a hard time finding any documentation on how to setup the snapshot portion, and also how to take advantage of it in a scenario like mine. Any ideas?

dzenz · Answer

Would you like to use the SATA side of the SAN as tiered storage or to simply host the snapshot change data to backup from?   Dave

OREOSpeedwagon · Answer

I'm not sure if I understand what you mean by "tiered storage", and not knowing really how the snapshot features work puts me further into the dark... :smileysad:

In my scenario, I have a MS DPM server and I thought I could attach it to the same SAN. I was hoping that it would be able to backup the virtual machines on the SAS side (that is mounted to other servers) to the SATA side using VSS, so I don't have to drag that data over Ethernet just to go on the other side of the SAN. Maybe this isn't how it works though?

I'd also be happy with a pure "snapshot" of that data in a flat format from one side to another. But then, I'm not sure how I would be able to schedule the backups w/ out DPM.

I'm hoping this makes sense!

OREOSpeedwagon · Answer

Sure, that makes sense. That was what I was thinking, of copying SAS data to SATA drives for backups. One of the things I was concerned about though was taking snapshots of the data, like running virtual machines, and then moving to SATA. I don't want to catch them in the middle of an I/O. That's why I was wondering about using DPM or how VSS fits in so we're not potentially corrupting this data while it's on the move.

dzenz · Answer

One use of 'tiered storage' is managing data across different performance/capacity levels of storage. For example, if data on the SAS side of the SAN is growing stale and doesn't need to be accessed on a continual basis then it can be moved to the SATA side that has lower performance but greater capacity. It sounds though that you would like to use snapshot to simply back-up the data on the SAS, for this either SAS or SATA disks can be used.  Snapshot works by setting aside a repository for data that has changed on the source virtual disk. This data repository only needs to be big enough to hold the changed data. This is called copy-on-write... data is copied to the snapshot when a write to the source occurs. VSS can be use if the backup application includes this support.  The best practice is to have a backup server which mounts the snapshot virtual disk to keep this activity off of the production server.  Does this help?  Dave

dzenz · Answer

To clarify, SAS data doesn't have to be copied to SATA drives for backup. A snapshot can be taken of SAS data to SAS drives and then backed up from that.

The point about ensuring that there is consistent data to snapshot/backup is important as there is no value in backing up inconsistent data.

How one arrives at consistent data (e.g. not in the middle of an I/O), is dependent on the application and usage.

For example, Microsoft provides backup integration via VSS for SQL and Exchange so that a VSS aware backup application and the MD3000i cooperate to ensure that the backup is consistent.

Dave

OREOSpeedwagon · Answer

@dzenz wrote:

To clarify, SAS data doesn't have to be copied to SATA drives for backup. A snapshot can be taken of SAS data to SAS drives and then backed up from that.

The point about ensuring that there is consistent data to snapshot/backup is important as there is no value in backing up inconsistent data.

How one arrives at consistent data (e.g. not in the middle of an I/O), is dependent on the application and usage.

For example, Microsoft provides backup integration via VSS for SQL and Exchange so that a VSS aware backup application and the MD3000i cooperate to ensure that the backup is consistent.

Dave

Right, I knew I didn't have to snapshot to a different drive architecture. I had bought 2 TB of SAS for storage and then 2 TB of SATA for snapshots of the SAS storage.

So, going back to the snapshot and consistency, that's my confusion. I know that the SAN will snapshot a volume on its own, but doing so may catch a VM in an inconsistent state (if I'm following you). So, that's why I'll need to use a VSS aware backup program, such as MS DPM. The problem is, I'm not sure about how they'll work together. I don't want to take a snapshot (using the SAN) and move it to another volume that is mounted to the DPM server.... Because at that point I'd already have a backup of that data, without needing DPM.

On the other hand, I wouldn't want to have DPM backup servers w/ data on the "other side" of the SAN, since then the DPM server would contact those servers, drag that data across the network, only to put it right back on the same SAN, just on a different volume.

See my dillema?

I have to be missing something here. I would think that between VSS, VDS, and the MD's snapshot abilities, I would be able to use DPM to do a backup of the data from another server on the SAN, and then copy it to another portion of the same SAN w/ out dragging it across the Ethernet network.

Am I smoking crack, or am I just missing something?

dzenz · Answer

Can you detail exactly what you would like to snapshot and backup?   Dave

dzenz · Answer

OREOSpeedwagon, please check your messages.   Dave Message Edited by dzenz on 03-06-2008 02:26 PM

OREOSpeedwagon · Answer

Sure!

What I'd like to do is to take a snapshot of some virtual machines running on a MS virtual server host. I'd love to be able to snapshot these VMs as they are running and have those snapshots stored to a different portion of the SAN, in case something happened either to the VM, the server hosting them, or even that disk group. Once that data reaches another portion of the SAN, I could use another product to move that data to longer term storage.

Does that help?

BTW, thanks for your help.

PowerVault

Using snapshots for backups on MD3000i?

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