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Re: [linux-lvm] Mirrored LV

Koen Vermeer a écrit :

I was thinking of using a mirrored LV as a easier to use alternative to
a RAID1 PV (with matching VG and LV). I tried to find the information I
need on how this works and how to set it up, but so far, I failed.

First, am I right in trying to use LVM in this way? I have two disks,
and I just want to mirror some LVs.

Second, I am confused by the apparent need to have this log stored on
another device. Actually, this doesn't seem true in two ways: There's
the option of having the log in memory and then the documentation only
says that the log is 'usually on a separate device'. Does that mean that
using a mirrored LV makes no sense on a system with two disks? Or should
I just keep the log in memory in this case? Or can I use another PV on
one of the disks? Should this be mirrored as well? What happens if I
loose that data?

From what I found when searching for answers, it seems that I'm not the
only one that's confused... But maybe my searching skills are just
lacking. Anyway, I appreciate any help and insights!

I confirm that you have to use 3 disks to mirror a VG with the actual version of software. At home, having enough disk, I use 3 disks to get my VG/LV mirrored and it works flawlessly since a couple of years. At work, we have mirrored the PV using 2 devices and the software RAID (md) and build the VG/LV on top of that. It runs flawlessly for 4 years I think (have to check the exact installation date...) So choice is yours...
HAve a nice day.
P.S. At home, I do not use the whole PV for my LV.
Each PV is split in two dissymitrical parts : a small 100 M partition and the rest of the device. The small partition is used for a software RAID (md) to hold the /boot. The rest of the disk as a regular PV used to build the mirrored VG/LV. This way, if one disk breaks I still can boot onto the remaining one. Of course, it is a manual boot but easier compared to searching a useable rescue CD and the correct kernel version. Think about it.

If the only tool you have is a hammer, you tend to see every problem as a nail.
                Abraham Maslow

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