Q: Partition offset setting vs displaying

Question

My customer has RHEL systems connected to CLARiiON storage. Per EMC recommendations, they have modified the offset of the partition start to 128 to align with the backend disk blocks. The default offset is 63 if I remember correctly. However, when I look at two different LUNs (one with the 128 offset and one with the default) I get different numbers:
</pre>$ sudo powermt display dev=all | grep Pseudo | egrep 'poweri|powerj' | cut -d= -f2 | awk '{ print "sudo fdisk -l -u /dev/"$1 }' | sh
Disk /dev/emcpoweri: 126.7 GB, 126701535232 bytes
255 heads, 63 sectors/track, 15403 cylinders, total 247463936 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/emcpoweri1 128 247449194 123724533+ 83 Linux
Disk /dev/emcpowerj: 134.2 GB, 134217728000 bytes
64 heads, 32 sectors/track, 128000 cylinders, total 262144000 sectors
Units = sectors of 1 * 512 = 512 bytes
Device Boot Start End Blocks Id System
/dev/emcpowerj1 32 262143999 131071984 83 Linux
$</pre>
As you can see the offset for emcpoweri shows the 128 offset that was set in fdisk when it was created. However, when emcpowerj was created it was left to default which should be 63 but it displays 32. So which is it? Is the default 32 but the default for the "b" advanced option 63? Or is fdisk confused?
(Are we not able it inject HTML into posts anymore? My tags are not being recognized)
Edited by: bobthesungeek76036 on Mar 22, 2012 8:06 AM

Answer 1

Using the { c o d e } tag (no spaces) before the first line and after the last line still works.
Or is fdisk confused?If the LUN or partition data changed behind the scenes (while the drive had a partition mounted) any changes won't be recognized until the disk is unused and then mounted again. Fdisk tries to alert you to this with its babble about "still using old table" when you write the modified partition table using its "w" command.
You may want to try to re-read the partition table:
# /sbin/partprobe /path/to/LUN-or-device
# /sbin/partprobe -sThis may help; check using:
# /sbin/fdisk -l /path/to/LUN-or-deviceHWH