Andy Smith wrote:
> Hi,
>
> On Fri, Mar 14, 2008 at 12:47:06PM -0000, Vic wrote:
>> It would be pretty pointless having a redundancy system that caused the
>> machine to fail if *either* disk dropped out...
>
> Not cause it to fail right away, just to require manual intervention
> on boot. Are you sure a vgscan / vgchange -ay will complete ok if
> there are mirrored LVs with bits missing? I'm sure it didn't used
> to..
>
I have recently built a 5 disk (320GB ea.) + 1 system disk - RAID 5
storage box with LVM2 on top, the traditional way and looking at the
advantages I may have made by simply using LVM2 Mirrors. It seems that for
stability and control the LVM2 on RAID5 is a better solution from a first
pass of the mirrored LVM documentation.
Commands like lvconvert -m1 vg00/lvol1 leave me wondering where the
mirrors end up?
Also to create an LVM mirror lvcreate -L 500M -m1 -n mirrorlv vg0
/dev/sda1 /dev/sdb1 /dev/sdc1 feels a little ambiguous, the command says
make a Logical Volume with sda1, sdb1 as a mirror (eq. traditional RAID1)
then store a mirror log on sdc1. So I'm left wondering if the mirror is as
optimised in terms of performance, storage and recovery from disk failure.
How can I control precisely where in the VG data that requires redundancy
resides, perhaps I've missed something, it is my first pass of the docs.
I managed to obtain a sustained data transfer rate from a non RAID5 disk
member to a RAID5 LVM2 partition on the same motherboard of about 54.1
MB/Sec with a 96G file cp, I wonder how an LVM mirror would perform.
In principle LVM mirror looks like it will make adding a level of
redundancy to any system easy, but to optimise the use of 5 identical sata
drives I am glad I used a Linux RAID5 with LVM2 on top. I have the option
of adding and removing another RAID$ at any time to the VolumeGroup with
the left over space in the box. The RAID5 with LVM2 was straightforward to
build with the RHEL5 installer.
Damian
--
Damian Brasher
www.diap.org.uk - Hyper-virtual auto-changer (Aiming...
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