I know it's my own fault but still...
The problem:
We've setup a simple server machine with a bunch of harddisks of 60 and 80 Gb.
With 6 drives and lvm(1) setup it provided us with a nice amount of storage space, of course there was always the risk of a drive going bad but I had thought that lvm would be robust enough to cope with that sort of thing (no I didn't expect redundancy or soemthing like that, just I would be able to access data on the surviving disks)
Alas a drive went bad (reallly bad, beyond repair so no chance of getting any data from it).
Ok time for plan B how do I access the data on this 'limp' lvm system.
Googling and reading the FAQ's there were 3 options:
1 replacing the disk with a fresh one (still the data would be gone, as well as the lvm volume data stuff)
2 install LVM2 and access the lvm in 'partial mode'
3 quick hacks to access the lvm with risk of hanging when data on the missing drive would be accessed.
Option 1:
tried with an extra drive to no avail, how does one get the metadata stuff back on such a drive ? I assume there is some kind of 'numbering' scheme internally in lvm so it knows which drive is mapped where.
Option 2:
Installed LVM2 tools. Still running with the old kernel it says on vgscan/pvscan that there is a lvm consisting of 6 devices with one missing. With vgchange it says (naturally) that it needs the device mapper stuff in the kernel.
Compiled a new kernel with devicemapper (1.03 and 1.05 tested) and then pvscan says something about data being inconsistent on devices hda and hdc and such. vgscan find some vague lvm stuff but at the end is says found 1 volume expected 0.. vgchange -ay -P exits with a segmentation fault. (whereas it runs without segfaulting on the kernel without the devicemapper)
Option 3: lvm can't be activated because it needs 6 and finds 5 devices...
Raah.. :-)
For now we let the system rest until lvm2 matures and maybe the tools will be there to rescue this set of disks, the data on the drives is about 300 Gb worth of music and part of the data is still on cdrom backup but much of the music was added later and must be restored/re-ripped from the original audio CD's..
On the lvm is ReiserFS as filesystem. With the missing drive and maybe partially reactivating the lvm, what is ReiserFS going to do after mounting it ?
So for our new server system:
What is the best way to make a 'reliable' lvm system ?
Is mirroring the most viable option or is raid 5 also usable, keeping in mind the number of drives you can normally connect to a PC motherboard (some boards, ours too, have an on board ide-raid controller which we used as a simple ide extension since the bios onboard was only the 'lite' version and handled 2 drives in raid config only)
On our system the OS was installed on a small 2Gb SCSI drive and 6 IDE drives were used for 'massive amounts of storage' with still two IDE places available.
LVM seemed an easy way to expand when needed..
If we used mirroring the total number of effective drives will be 8/2 and the drives would have to be the same in pairs.
Upgrading the lvm would mean that 1 IDE port must be free to hook up a new (larger) set of drives, pvmove the data from the old (smaller) pair of drives we wish to replace to the new set and removing the smaller set out of the lvm.
But how about raid 5 ?
With raid 5 it is possible to hook up say 7 drives with 1 spare But then the upgrade path is almost impossible since all the drives have to be the same size for raid 5 to work...
Can anyone shed some light on this ?
Gert van der Knokke
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