RAID0 versus Linear

RedHat Advanced Server 2.1AS
Raidtools-1.00.2-1.2

Couldn't seem to find anything relevant in the linux-raid archive...

Had an internal discussion regarding the choice of linear versus raid0.  We'd like to standardize on a usage within our company.

(If this makes a difference: We have a SAN which will present a host with a disk using SCSI over fibre.  (That's the extent of my SAN-technical jargon/knowledge.).  The virtual disk presented to the host is a 0+1 RAID volume on the other end which is supposed to be transparent to the user/host system.)

Disks will not necessarily always be of the same size, but we do want to concatenate them, so I guess linear would be the way to go.  Problem is I built a RAID0 array during testing, and was now trying to convert it to linear, by simply:
*editing the /etc/raidtab file appropriately: raid-level 0-->raid-level linear
*umount /raid_dir
*raidstop /dev/md0
*mkraid -R /dev/md0

I would assume that this is the appropriate procedure, but I get a nasty kernel crash, of which I don't have anything able to capture it.

(Tried different combinations of enable/disabling the persistent-superblock.  I've not been able to reproduce it regularly, but was getting errors that "persistent-superblock was not supported by linear or RAID0" at various times during the boot process, but once I redid the md device with a mkraid, and built a new fs, it seemed to be OK.  The logs complained about an invalid superblock on the device 0 everytime.)

I'd also like to confirm that RAID0 can only be used for disks of aproximately the same size.  If they aren't, does the extra space become unusable?

Marco

On Mon, 23 Sep 2002, Shaw, Marco wrote:

be OK.  The logs complained about an invalid superblock on the device
0 everytime.)

If it's still broke, send the log entries, kernel version, etc.

I'd also like to confirm that RAID0 can only be used for disks of
aproximately the same size.  If they aren't, does the extra space
become unusable?

RAID-0 can use disks of varying sizes and will stripe data across
remaining disks when individual drives fill up.

---
Derek Vadala, derek@cynicism.com, http://www.cynicism.com/~derek