LVM mirroring & EMC BCV restore

[Nagarjuna]

Hi,

I have a Host based mirroring( HP-UX mirroring)of R1 and R2 and a BCV on R1 for backup of datbases and other BCV set on R2 for database backups. The data on R1 & R2 got corrupted after few hours of the last backup taken on R1 BCV.

Question:

When i restore from the R1 BCV to R1 without spliting the mirrors between R1 & R2, Will the writes happen from R1 to R2 while restore?

OR

LVM forces R2 to write to R1 as the timestamp on R2 is new compared to R1 as the backup is few hours older.


Thanks & Regards,

Nagarjuna.K

[Steven E. Protter]

Shalom,

It would be helpful to know how you mirrored. I'll assume it was mirror/ux

If you have a valid mirror on R1 and you stop the database and restore the data it should be restored to both mirror copies.

lvdisplay -v

The confusing part here is that you have an EMC array and you did some kind of backup on that. Assuming its a valid snapshot using the features of the aray, it should be usable.

The fact that you are using host based mirroring of the data when you have an EMC array is a mistake and will not help recoverability or performance.

The EMC array handles mirror copies without using CPU and lessens the overall I/O system assuming the array is properly configured.

There is a lot however you are not providing us in order to help you. The general rule however is OS striping/mirroring on top of hardware striping/mirroring provides few benefits and should not be done.

More details please.

SEP

[Nagarjuna]

Thank you very much for quick reply.

We are using mirror/UX for mirroring of data across datacenters . We have two PVG groups . Each group contains a set of disks from one array and other set on disks on the other array and lv are created with PVG strict.

eg PVG1 has disks on array 228 and PVG2 has disks on array 224. 224 and 228 arrays are sitituated at different locations and host trapazium can see both the arrays disks.

We have a BCV1 set on 224 which are attached to disks on 224 in a device group 224BCV1.
We have a BCV2 set on 228 which are attached to disks on 228 in a device group 228BCV1.

We rotate the backups on the BCV1 & BCV2 set . Morning we take backup on to 224BCV1 and evening we take backup on to 228BCV1 using Symbcv estabish/split by blocking the database activity so that the backups were consistent.

We dont have EMC SRDF to do array level mirroring.

The BCV copies are consistent.

If i split the Host based mirroring ie , lvspit the the logical volumes and then do a restore on the respecitve PVG disks

Eg: If if reduce PVG2(228) sothat PVG1 will the disks( 224) I am restoring to using 224BCV1 on to 224 disk and start the database, it comes up fine without any problems. And later I can do lvmrge. The restore is done using symbcv restore.

If i do a restore from the 224BCV 1 on to 224 disks with out spliting the Host based mirroring between the disks on 224 and 228 array the database dosent come up . So I think the disks on 228 which are having corrupted data and current timestamp compared to the 224BCV1 is overwriting the data restored from 224BCV1 onto R1.

I am not sure of how lvm works internally. Correct me if I am wrong. Any ideas will be much helpful.

Is it possible to restore the data without lvsplit/lvreducing the mirror. Is there a way to force the writes from one PVG to other PVG in Mirror/ux without spliting the mirrors.

Thanks & Regards,

Nagarjuna.K