Mirroring

[Alan Bocutt]

We are soon to be installing an 'N'class with a number of scsi and fibre
channel disks all 18GB disks if we create 18GB volumegroups and then mirror
them across to devices is there a way of estimating the time for there
re-syncronisation

[Carlos Riera]

When you do mirror, you do just for defined lvs not for all disk, so mirroring
vg01 must take more or less time than vg02, depending of amount of LE to
mirror.

But you can use a trick, so firt define just 1 Logical extension for each lv
you must define, and then make mirror of each volume.. at end extend each
logical volume to its logical extensions. With this trick mirror time is near
to 0.:

lvcreate -L 1 /dev/vg01/lvol1
lvextend -m 1 /dev/vg01/lvol1
lvextend -L 2000 /dev/vg01/lvol1
....

[Alan Bocutt]

My apologies I should have been more specific what I was actually after is a
way of estimateing the amount of time it would take to re-synchronise them
after we had split the mirrors for a cold backup

[Alan Riggs_1]

The only accurte way to estimate the time is to run tests on teh system/disks
in question (or a test system with close to identical use/configuration).
Split the mirror on a 1Gig lv, for instance, and then remirror. Also, other
system usage may affect teh resync time by competing for access to buffer
cache, I/O bus, disk controllers, etc.

[Carlos Riera]

Im sorry.

Resyncronization time, of a previously splited lv, is variable and in relation
of the amount of modified data.

When you split a lv, LMV creates a map of modified LEs. When merge LVM
overwrite those, only.