Does mdadm work on active/passive arrays
Hi,
Just a small question about creating multipath devices using mdadm:
Does it support Active/Passive Arrays like the Clariion?
I am using mdadm v1.11.0, and the devices return no UUID when queried using mdadm -D --scan.
dmesg has a lots of entries like:
md: write_disk_sb failed for device sdf
md: errors occurred during superblock update, repeating Device 08:50 not ready.
BTW, I am using qla2300 modules with options scsi_mod max_scsi_luns=255 scsi_allow_ghost_devices=1.
Thanks in advance,
--AM
Quoted 3 lines · Anu Matthew
Just a small question about creating multipath devices using mdadm:
Does it support Active/Passive Arrays like the Clariion?
This is not a function of mdadm, but of the md multipath code in the kernel. The short answer is: "No".
md multipath is not being actively developed and extended in 2.6 any longer.
However, there is hope. The Device Mapper multipath module _does_ support the EMC CLARiiON CX-family of arrays quite well (in fact, I'm developing with one). At least in the latest udm patchsets by Alasdair, and in combination with the multipath-tools userspace package.
The multipath support in SLES9 SP2 will be based on this, and to my knowledge also that in RHEL4 U1, but I can only guess about that ;-)
The latest tools are basically zero config on those arrays: Just start it and it'll do the right things. For SLES9, we'll publish a Support Database Article in time with the release. (Because obviously the actual integration into the distribution differs slightly.)
You can find more information about DM MPIO at
http://sources.redhat.com/dm/.
Quoted 2 lines · That
I am using mdadm v1.11.0, and the devices return no UUID when queried using mdadm -D --scan.
No wonder; mdadm tries to read the md superblock of the disk, which is not possible for a passive path on an EMC CX. You first need to send the SCSI trespass command to re-bind the Logical Unit to that Service Processor. (Which at the same time makes it inaccessible on the other SP...) mdadm and md multipath don't know about that and can't handle it.
Quoted 2 lines
BTW, I am using qla2300 modules with options
scsi_modmax_scsi_luns=255 scsi_allow_ghost_devices=1.
FWIW, I also recommend
options qla2xxx qlport_down_retry=1 ql2xfailover=0 ql2xretrycount=5 to faciliate fast switch-over in case a path fails.
At least it seems to work fine during my testing so far ;-)
Sincerely,
Lars Marowsky-Brée <[email protected]>
Signature · 8 lines
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