6TB storage expansion

Introduction

56 instead of 50TB are now available for the bioinformatics cluster. The tasks required to realize this extra space are:

• rescan multipath, details: multipath WWID; 36000d3100051f800000000000000016e (on mpathd)

Tools

listing

multipath -l

will give a useful if not very understandable list of characteristics. Most important, the device: dm-6 is noted, i.e.

mpathd (36000d3100051f800000000000000016e) dm-6 COMPELNT,Compellent Vol
size=50T features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  |- 6:0:0:1 sdd 8:48 active undef running
  |- 7:0:1:1 sde 8:64 active undef running
  |- 6:0:1:1 sdg 8:96 active undef running
  `- 7:0:2:1 sdf 8:80 active undef running

configuration

/etc/multipath.conf

Doesn't really have much. The only actives are:

defaults {
   user_friendly_names yes
}

blacklist {
    wwid 3600605b006c5f11019eadc840e589ae9
    wwid 3600605b006a1af8019ee9a2d1036bfa7
    wwid 3600605b006a1af801b46c4773d54b7d4
}

interpreter

There is also a interpreter available to query status and other things. To fire it up, type

multipathd -k

The

show maps topology

command in this interpeter will give you the same output as the "multipath -l" command. It mayy be necessary to find out more about the tool. For example, this command

paths count

gives 4 as the answer, which probably refers to sdd, sde, sdg, sdf mentioned in the above output. Indeed the

show devices

gives these four as the output. Unfortunately, there is nothign about rescanning here. I think this tool is at a higher-level than what is required for the rescanning, which seems to be a lower level jobs (multipath's understanding of "devices" gives this away somewhat).

Indeed thsi tool will be useful for resizing, but unfortunately not for rescanning.

Procedure

The rescan operation is most definitely required. Both Red Hat and Ubuntu guides give the same method of doing this

# echo 1 > /sys/block/device_name/device/rescan

However, under /sys/block/dm-6, there is no device subdirectory, and, needless to say, no rescan file. Mind, this is for SCSI.

Other sites repeat the recipe ad nauseam. There is no mention about whether this can in fact be done live.

Links

• Red Hat DM-Multipath guide
• ubuntu troubleshooting guide to DM-Multipath
• Kristian Reese's LUN solution