Apple Xsan 2 (Third Edition) - Manual (Page 103)

Chapter 8 Solving SAN Problems 103
If Fibre Channel Performance Is Poorer Than Expected
Mismatched optical transceivers (GBICs) can cause Fibre Channel communication
errors and degrade SAN performance. To ensure good performance, use identical
transceivers (same manufacturer and model number) on both ends of your Fibre
Channel cables.
If a Client Can’t Use a Volume After a Fibre Channel
Interruption
If a client loses its Fibre Channel connection to the SAN (for example, because a
cable is unplugged), the client might not recognize LUNs in an Xsan volume after the
connection is restored. If this happens, restart the client to remount the volume.
If problems persist, restart all SAN devices. Restart RAID systems first, then continue
with SAN controllers, and finally, restart all clients.
To check whether a computer is seeing Xsan volume LUNs:
Open Disk Utility on the computer and look for the LUNs in the list of disks and
m
volumes.
From the Command Line
You can also check for accessible LUNs using the
cvlabel -l command or the
diskutil list command in Terminal.
If You Can’t Add LUNs to a Storage Pool
You can’t add a LUN to a storage pool unless the LUN is at least as large as the smallest
LUN you added when you created the pool. You can add a larger LUN, but space
beyond the smallest LUN size isn’t used.
You can only expand storage pools that can be used for user data. You can’t add a LUN
to a storage pool if the storage pool can be used only for journaling and metadata.
To add journaling and metadata storage, add another storage pool that can be used
for journaling and metadata.
Also, Xsan Admin won’t let you to add a LUN to a storage pool if adding the LUN will
fragment the storage pool so much that performance suffers.
To check the common LUN size for a storage pool:
In Xsan Admin, select Volumes in the SAN Assets list and then click disclosure triangles
m
in the list of volumes to show the LUNs in the storage pool of interest. Compare the
listed LUN sizes.