It has been seen in the field that some array vendorsachieve the Dynamic LUN Expansion (DLE) operation in different ways.
It willbe known by NetApp Filer users, that this vendor array enforces a Maximum LUNResize limit.

The 'vxdisk resize' works by keeping cylinder size (no ofheads * total no of sectors per track) constant before and after resizeoperation unless the no. of cylinders go beyond 2^16-1 (65535)

This isdone so that when resizing the LUN, the Cylinder geometry doesn't change, andthe Sectors/Cylinder value remains the same.

In a recent case involving3PAR storage, it was seen that the Sectors/Cylinders (Heads) value changedduring a DLE grow operation, resulting in the Sectors/Cylinderincreasing.

As a result of this LUN geometry change, VxVM is unable tocomplete 'vxdisk resize' on simple and sliced format disks. VxVM was notdesigned to handle such geometry changes during DLE operations on simple/sliceddisks.


SIMPLE DISK HAVING ISSUES:

# vxdisk list | grepmydg | grep d5
c1t500A098198AC4917d1s2 auto:simple    d5           mydg        online

ERROR:

# vxdisk -g mydg resize d5
VxVM vxdiskERROR V-5-1-8643 Device d5: resize failed: Invalid data inrequest

WORKAROUND:

The VxVM "vxdisk resize" code behavesdifferently depending on whether the disk is simple, sliced, or CDS.

Theproblem shown above, only occurs on simple and sliced disk configurations. As aresult of this difference in behaviour, if the geometry changes during a DLEoperation at the LUN level, the 'vxcdsconvert' command can be issued on the diskallowing the "vxdisk resize" command to succeed.

Before starting on usingthe workaround, there is a caveat that must be made clear. On VxVM versionsbefore Solaris 5.1SP1, the CDS layout has a limitation in that it cannot supportLUNs greater than 1 Terabyte in size. As a result of this limitation, we cannotconvert such disks to CDS to workaround the 'vxdisk resize' limitation describedin this document. If 5.1SP1 is available, it would be recommended that customersupgrade/patch to this level before attempting to convert > 1Terabyte LUNs toCDS layout with vxcdsconvert.

CHECK SIZE OFDISKS:

#  vxprint -htg mydg -d d5
DMNAME         DEVICE       TYPE    PRIVLEN  PUBLEN   STATE
dm d5          c1t500A098198AC4917d1s2 auto 65536 125761008 -   <-- ORIGINALSIZE

CONVERT THE SIMPLE/SLICED DISK TO CDSDISK:

#vxcdsconvert -g mydg disk d5

SEE THAT DISK IS NOW "cdsdisk":

# vxdisk list | grep mydg | grep d5
c1t500A098198AC4917d1s2auto:cdsdisk    d5          mydg         online

GROW THE DISK inVxVM:

# vxdisk -g mydg resize d5

CONFIRM THE DISK HASGROWN:

#  vxprint -htg mydg -d d5
DMNAME         DEVICE       TYPE    PRIVLEN  PUBLEN   STATE
dm d5          c1t500A098198AC4917d1s2 auto 65536 188641024-             <---- BIGGER


We expectthat this limitation on 'vxdisk resize' and simple/sliced disks will bedocumented in future release, and possible code inserted to provide a more userfriendly message regarding the unsupported LUN geometry change in the StorageArray.