restore vg using dd

[Matthew Pegge_1]

I have a pre-upgrade LUN copy of my applcation volume group LUN, that I wish to recover to. I.e regress applciation to pre-upgrade. I am thinking the easiest way to do this is via dd. high level process...

1. mount both vg11 and vg11_copy
2. newfs all vg11 file systems
3. dd if=/dev/vg11_copy/rlvolA of=/dev/vg11/rlvolA
4. dd if=/dev/vg11_copy/rlvolB of=/dev/vg11/rlvolB
5. And so on.
6. Unmount vg11_copy

2 questions. Is this the best way to do this... and if so what block size should I use, it's a 40Gb volume.

[Pete Randall · Accepted solution]

Matthew,

It sounds feasible. Make sure you use the raw logical volumes (as you showed). For block size, I would use 1024K.

dd if=/dev/vg11_copy/rlvolA of=/dev/vg11/rlvolA bs=1024k


Pete

[Pete Randall]

Matthew,

It just occurred to me - you need to ensure that your logical volume definitions are identical. They probably are but just in case . . . .

Pete

[Matthew Pegge_1]

by that I take it you mean lv sizes etc...

[Pete Randall]

Exactly. How was your LUN copy produced? By dd, I hope.


Pete

[Matthew Pegge_1]

It's a lun on an eva, created using business copy - a snapclone.

[Pete Randall]

Hmmmm, I'm not familiar with business copy but it still seems reasonable if it's an exact copy. I don't suppose business copy has a business resore function, does it? Or could you just business copy back, rather than dd?


Pete

[Matthew Pegge_1]

I wish!! That's why I'm asking this question unfortunately! The VA version of business copy did... but I'm told there is no such functionality on the EVA.. which sucks as apart from this issue the EVA's are a fantastic product!

[Matthew Pegge_1]

One last question then... I'm testing the speed of this by setting the of=/dev/null.. how realistic will the timings be compared to writing it to actual disk? This is taking 2.5 minutes to dd 40Gb which is fantastic!!

[Pete Randall]

I expect it will be a bit slower when you're actually writing to disk, but it's just a sequential dump so it's pretty quick.


Pete

[Devender Khatana]

Hi Mathew,

There is a option of reverse sync in business copy & we have even tried this with our XP1024. If your EVA is supporting business copy then it should also support reverse copy, just cros check it.

Moreover for copying 40Gb of data through dd should atleast take 5-6 Minutes. This is what is takes in our case with XP1024. Just share the exact time once you are finished with activity.

HTH,
Devender