Software RAID configuration in RHEL 3.0 AS

[shreejesh]

Dear all,
I am having two Intel servers loaded with RHEL 3.0 AS. They are clustered together with a SAN storage. In each of the servers there are two HDDs ( sda & sdb). Both are mirrored each other and the servers show the patitions in the storage also. The problem is when I remove my first mirrored HDD (sda) the second one (sdb)becomes sda and all the other ( storage) partions are shifted above thus disturbing the cluster and applications.Please guide me to solve this issue.

Regards.
shreejesh.

[Steven E. Protter]

Shalom sreejesh,

You need to follow this general outline.

1) Use fdisk to partition the the new disk.
2) run the mdam command to rebuild the mirrors.


Here is a check script:

/bin/cat /proc/mdstat
mdadm -D /dev/md0
mdadm -D /dev/md1
mdadm -D /dev/md2
mdadm -D /dev/md3
mdadm -D /dev/md4
mdadm -D /dev/md5


SEP

[Serviceguard for Linux]

Which clustering SW are you using?

Most of the SW clusters on Linux that I am familiar with do not support using SW RAID. You certainly cannot have the same SW RAID luns active on more than one node at a time.

[Devender Khatana]

Hi,

It seems that the software raid is used only for OS mirroring and cluster is not used for software mirror on the LUNs.

This is a interesting problem and I would be interesting in the ways of overcoming this issue apart from putting a dummy disk and making it hdb to keep the storage naming same.

Does LVM for linux help on this?

-Devender

[shreejesh]

Dear Potter, I have already done the mirroring using the fdisk and /etc/raidtab.I am not including the SAN Array partitions for mirroring. Also I am using RH cluster if is of least importance. If problem is if sda fails, sdb becomes sda, sdc becomes sdb, etc..which spoils the cluster and other configurations. Please help me out in this.....Regards,Shreejesh.

[Ivan Ferreira]

That is normall, and until now, I don't know a way to do persistent scsi disk mappings to devices in red hat (SUSE does it).

You should not remove and reboot the disk, you could change the disk hot swap, or always reboot with the replacement disk already.

[Stuart Browne]

I guess one way would to not rely upon the SCSI ordering to begin with.

Filesystems can use the Label's to identify which is which, and I'm pretty sure you can do a similar thing with the software raid.

... but reading the documentation on an ES4 box sort of indicates that's not possible ...

Righteo then, I'd suggest reading the following two URL's:

http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO/dnames.html
http://www.garloff.de/kurt/linux/scsidev/

This may give you an idea on how to proceed.

Bascially, 'scsidev' is a tool which creates device nodes based on SCSI ID's rather than on their order. The other option is to use a 'devfs', but I'm unsure how to go about that on an AS3 system. (the other seems less intrusive).

Hope this helps.