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Troubleshooting issues with extents has never been easy. If one extent member went offline, it has been difficult to find which physical LUN corresponds to the extent that went offline. vSphere 5.0 introduces the ability, via vmkfstools, to check which extent of a volume is offline. For example, here is a VMFS-5 volume I created which spans two iSCSI LUNs:

~ # vmkfstools -Ph /vmfs/volumes/iscsi_datastore/
VMFS-5.54 file system spanning 2 partitions.
File system label (if any): iscsi_datastore
Mode: public
Capacity 17.5 GB, 16.9 GB available, file block size 8 MB
UUID: 4d810817-2d191ddd-0b4e-0050561902c9
Partitions spanned (on “lvm”):
        naa.6006048c7bc7febbf4db26ae0c3263cb:1
        naa.6006048c13e056de156e0f6d8d98cee2:1
Is Native Snapshot Capable: NO
~ #

Now if something happened on the array side to cause one of the LUNs to go offline, previous versions of vmkfstools would not be able to identify which LUN/extent was the problem, and if investigating from the array side, you would have to look at all the LUNs making up the volume and try to figure out which one was problematic.  Now, in 5.0, we get notification about which LUN is offline:

~ # vmkfstools -Ph /vmfs/volumes/iscsi_datastore/
VMFS-5.54 file system spanning 2 partitions.
File system label (if any): iscsi_datastore
Mode: public
Capacity 17.5 GB, 7.2 GB available, file block size 8 MB
UUID: 4d810817-2d191ddd-0b4e-0050561902c9
Partitions spanned (on “lvm”):
        naa.6006048c7bc7febbf4db26ae0c3263cb:1
        (device naa.6006048c13e056de156e0f6d8d98cee2:1 might be offline)
        (One or more partitions spanned by this volume may be offline)
Is Native Snapshot Capable: NO
~ #

In this case, we can see the NAA id (SCSI identifier) of the LUN which has the problem and investigate why the LUN is offline from the array side. A nice feature I’m sure you will agree.

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~ # vmkfstools -Ph /vmfs/volumes/iscsi_lun0/

VMFS-5.54 file system spanning 2 partitions.

File system label (if any): iscsi_lun0

Mode: public

Capacity 17.5 GB, 7.2 GB available, file block size 8 MB

UUID: 4d810817-2d191ddd-0b4e-0050561902c9

Partitions spanned (on “lvm“):

        naa.6006048c7bc7febbf4db26ae0c3263cb:1

        (device naa.6006048c13e056de156e0f6d8d98cee2:1 might be offline)

        (One or more partitions spanned by this volume may be offline)

Is Native Snapshot Capable: NO

~ #

About the Author

Cormac Hogan

Cormac Hogan is a Senior Staff Engineer in the Office of the CTO in the Storage and Availability Business Unit (SABU) at VMware. He has been with VMware since April 2005 and has previously held roles in VMware’s Technical Marketing and Technical Support organizations. He has written a number of storage related white papers and have given numerous presentations on storage best practices and vSphere storage features. He is also the co-author of the “Essential Virtual SAN” book published by VMware Press.