snapshot and restore.

[samaoas]

what is the procedure to create snapshot in eva 4000. i have business copy license in eva4000 and installed in command view. how to create snapshot. how to restore the snapshot, restoring the snapshot is a online activity or offline activity.. someonecan explain this.

[samaoas]

will anyone reply

[Víctor Cespón · Accepted solution]

How about some reading?

Command View user guide:

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c02010669/c02010669.pdf

Select the vdisk, select "create snapshot", select "demand allocated" or "fully allocated", select the RAID level for the snapshot.

To restore from a snapshot, select the a vdisk that has snapshots and then select restore. It's instantaneous as any data copy is done in the background.

[Navaneeda]

how the snapshot works, when i take a snapshot of a disk what is actually copied. i need more info on snapshot.

[Víctor Cespón]

A snapshot stores only the changes from the moment you created it.

If you access a sector that has not changed, the info is read from the original vdisk.

If you write to the vdisk, the sector you're going to overwrite is copied to the snapshot, then the new data written to the vdisk.

This way the snapshot contains a copy of the data as it was in the moment it was created.

[samaoas]

in this way what is the use of creating snapshots. for example i have a 60Gb of disk and i have created a snaphot at 10.30. so once the smapshot is created, then the new data which is going to add on the virtual disk are written to the snapshot and then writtent ot the virtual disk ?.. in this method will there be any perfoamcne issues.. as it is writing first in snapshot and writing in virtual disk....
Basically what is the benifit we wil get with snapshot. how to backup this snapshot...

[Uwe Zessin]

Yes, there will be a performance hit the first time a data block on the original disk is replaced, because the EVA must first read the old data, save it in a different area in the disk group and update the snapshot pointer.

As vcespon wrote: a snapshot is a mix of unchanged data from the original virtual disk and saved data, because the area in the original was overwritten since taking the snapshot.

So if you present the snapshot to a server it will give you a complete look of the original file system at the time you took the snapshot.
You can delete some files from the original disk, but if you look into the snapshot filesystem they will still be present. The EVA has retained that data.

One of its uses is that you can access old data quick without a restore from tape. With a 'snapshot restore' you can even 'switch back' the whole original virtual disk.

Or you can run the disk agent from your backup software against this snapshot. There won't be any open files and no inconsistencies as would happen on a 'life filesystem'.

[samaoas]

so i understood the below.
if i have a 40gb virtual disk and when i take a sanaphot at 10 Pm, it just copies the pointers for the blocks on the virtual disk at 10 PM that time.. Anfter the snapshot when the oroginal disk is getting updated,,, .. so when i restore the 10 PM snapshot... at 12 PM on the updated original virtual disk ,, then after the snapshot restore i will have the 10 PM Data on my virtual disk. Is that correct ??

How to backup the snapshot.. is there any license required ,

[Víctor Cespón]

When you create the snapshot, the EVA just creates a table of pointers to the blocks that form the source vdisk.

When you write to the vdisk, that block is copied to the snapshot to preserve it as it was. Then the new data is written to the vdisk.

If you choose to restore from the snapshot, then all blocks that were saved are copied to the vdisk, leaving it as it was at 10 PM.

If you present a snapshot to a host, it looks like any other vdisk. It will read data from the source vdisk if it has not been modyfied, or from the saved blocks if it has been modyfied.

You can backup it as any disk on the server. The advantage of course is that it's contents do not change. That's the idea of a snapshot after all.

[samaoas]

thanks for the reply, so snapshot can be used to capture the point in time blocks..

for example , when i create a snapshot at 10 PM for a virtual disk , will the snapshot created immediately or the snapshot will be on till we stop it ??

i have created a snapshot and after the creation some reason my source virtual disk data is corrupted.. so in this scenario, can i use my snapshot to recover my entire vdisk corrupted data back to normal ??

how much disk space is required to cretae a snapshot for 60 GB disk ?