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I have been given 4.8T of SAN storage to my Ubuntu 10.04 64Bit server. multipath only sees 2.0T. Is this a limitation of Ubuntu or Multipath; or am I doing something wrong?

Example output:

36000d77a0000974f6367a370c8e09342dm-3 FALCON  ,IPSTOR DISK
[size=2.0T][features=0][hwhandler=0]
\\_ round-robin 0 [prio=1][active]
 \\_ 1:0:2:2 sdr 65:16 [active][ready]
\\_ round-robin 0 [prio=1][enabled]
 \\_ 0:0:2:2 sdi 8:128 [active][ready]
\\_ round-robin 0 [prio=1][enabled]
 \\_ 0:0:3:2 sdl 8:176 [active][ready]
\\_ round-robin 0 [prio=1][enabled]
 \\_ 1:0:1:2 sdo 8:224 [active][ready]
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1 Answer 1

I am going to assume that this is an iSCSI LUN. What you might have an issue with is partitioning on this device. Consider using parted to partition this device, and see if the size of the device changes. If this LUN is going to be deployed with LVM+DM-Multipath, consider splitting this one LUN into smaller LUNs, which will allow for a normal MSDOS partition table, instead of (GPT) GUID partition table, and then simply adding all LUNs to the same volume group under LVM. This is a more sane approach, and makes life easier in the long run. On larger servers with several hundred LUNs we routinely take this approach to simplify administration, and allow for traditional partitioning, instead of using GPT.

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yes it's iSCSI. I'm not sure it's a partitioning problem: I used parted and it didn't make a difference; and if I understand things correctly, multipath works on a layer below partitions and thus should not care about this. –  user7054 May 31 '11 at 22:42
    
It doesn't matter that it's iSCSI, you've hit the MS-DOS partition limit (2TB) and must convert to GPT. rodsbooks.com/gdisk/mbr2gpt.html If you also resized these devices while they were online then you'll also need to inform multipath of this. See: docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/… –  ppetraki Nov 21 '11 at 15:27
    
Yes, multipath works directly with block devices for pathing but it must also present each partition you defined and that's where you're seeing the problem. Multipath is simply passing through the partition limitations MS-DOS style partitions have defined. If you removed multipath and tried examine the active disk you would observe the same limitation. –  ppetraki Nov 21 '11 at 15:32
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