Advantage of Export/Import over Rebuild

[Philip P. Hartl]

Almost inevitably whenever an upgrade or disk replacement is discussed the recommendation is to export the volume group prior and import following the procedure. If you must do a data restoration anyway, what is the advantage to export/import over simply removing the old VG structures and recreating them prior to restoring the data?

[John Poff]

Philip,

The advantage of the vgexport/vgimport method is speed. You don't have to recreate anything. You just import the vg and mount it up. This really helps in my environment, as a vgexport/vgimport can be done in a couple of minutes versus 6 to 8 hours for a full restore.

Plus, with a restore you take the chance of sending all your bits through the path from the tape to the disk. It usually works, but Dr. McCoy had the right idea; why scramble all those atoms if you don't have to?

JP

[John Palmer · Accepted solution]

Hi,

There's no advantage in export/import if you intend restoring data. You may as well recreate the volume group(s).

export/import means that you don't have to restore any data. The original contents of the disk(s) remains unchanged. import simply adds details of the volume group to the system so that you can activate it.

Regards,
John

[Bill McNAMARA_1]

vgex and vgim. don't require rebuilds, under normal use... however if a disk fails and you've replaced a disk, vgcfgrestore is the only way to replace the lvm lvol information.
The replaced disk will not have any data on the disk describing the lvm structures of the vg pv it is replacing.

When a disk fails you have no alternative but to restore the data.

If you're not sure what data you lost, or what filesystem because corrupted, in that case you may find it quicker to restore the entire vg... but you should know... you are the administrator afterall!

Later,
Bill

[Philip P. Hartl]

Thanks for the responses. You have confirmed what I suspected, but thanks to the responses I see there is a definite use for VGIN/VGEX.