To ensure maximum stability, you should manually label LUNs greater than 2TB when using Xsan versions 1.0 to 1.2 only (Xsan 1.3 and later running on Mac OS X 10.4.5 or later will support LUNs of 2TB and larger).
When you introduce a LUN that's larger than 2TB to an Xsan volume, Xsan Admin reduces the size, or "Sector count," of the LUN to 2TB worth of sectors. Xsan Admin accomplishes this reduction during the naming, or "labeling," of LUNs in Xsan Admin > Setup > LUNs. Instead of using Xsan Admin to label these larger LUNs, you can use the instructions in this article to manually configure the LUNs via the Terminal&emdash;this is the preferred method in Xsan 1.2 and earlier, because it allows you to specify a custom sector count size, 4294965247, which is a slightly smaller amount of sectors than the Xsan Admin application configures. The slightly smaller sector count is recommended for LUNS which will be added to new Xsan volumes or for LUNs that are to be added to pre-existing volumes. Labeling LUNs in this manner avoids certain scenarios that result in instability.
WARNING: These steps can only be performed on LUNs which are not already part of an Xsan volume. Performing these steps on LUNs that are currently included in an Xsan volume will cause all data to be lost on the Xsan Volume. Additionally, these steps will erase any data currently stored on the LUN. Therefore, you must back up all data on the LUN before proceeding.
In the Terminal application, issue the following command to Identify the LUN(s) that you wish to configure:
$ sudo cvlabel -l
Example results:
/dev/rdisk3 [APPLE Xserve RAID 1.26] unknown Sectors: 4724464025. SectorSize: 512. /dev/rdisk5 [APPLE Xserve RAID 1.26] acfs "Big_RAID5-2" Sectors: 4724464025. SectorSize: 512. Maximum sectors: 4724464025.
This output indicates that there are two available LUNs, /dev/rdisk3 and /dev/rdisk5. Note by the sector count of 4724464025 that both LUNs are larger than 2TB (this is more than 2TB's worth of sectors). /dev/rdisk3 is designated as "unknown" and therefore has not been configured for use with Xsan, while /dev/rdisk5 has been configured for use with Xsan and labeled "Big_RAID5-2." To reconfigure a LUN which is already configured for use with Xsan, issue the following command in the Terminal:
$ sudo cvlabel -u <DeviceName>
Where <DeviceName> is the name of the volume to be unlabeled. For example, to unlabel /dev/rdisk5 in our example, you would issue this command:
$ sudo cvlabel -u Big_RAID5-2
Before we proceed with configuring the LUNs with new labels, we’ll verify that both LUNs have been unlabeled:
$ sudo cvlabel -l
Example results:
/dev/rdisk3 [APPLE Xserve RAID 1.26] unknown Sectors: 4724464025. SectorSize: 512. /dev/rdisk5 [APPLE Xserve RAID 1.26] unknown Sectors: 4724464025. SectorSize: 512.
Both LUNs have been unlabeled, as they both are designated as "unknown."
Issue the following command in the Terminal to create a temporary file containing the configuration information for the LUN:
$ cat > /tmp/lun-label-info
This command creates a temporary file in the /tmp directory which you will edit by entering text in this format:
<LUNname> /dev/<rdiskNumber> 4294965247For example, you might type:
HugeLUN1 /dev/rdisk3 4294965247
HugeLUN2 /dev/rdisk5 4294965247
When you finish typing in the data, press Control-D on the keyboard.
Issue the following command in the Terminal to configure the LUN:
$ sudo cvlabel /tmp/lun-label-info
Example output:
*WARNING* This program will over-write volume labels on the devices specified in the file "/tmp/lun-label-info". After execution, the devices will only be usable by the Xsan. You will have to re-partition the devices to use them on a different file system.Do you want to proceed? (Y / N) -> y/dev/rdisk3 [APPLE Xserve RAID 1.26] unknown Controller '5000393000001723', Serial '5000393000001723L1', Sector Size 512, Sectors Max 4724464025 (2.2TB)
Do you want to label it acfs-VTOC - Name: HugeLUN1 Sectors: 980416512 (Y / N) -> y New Volume Label -Device: /dev/rdisk3 acfs Label: HugeLUN1 Sectors: 4294965247.
Do you want to label it acfs-VTOC - Name: HugeLUN2 Sectors: 980416512 (Y / N) -> y New Volume Label -Device: /dev/rdisk5 acfs Label: HugeLUN2 Sectors: 4294965247.Done. 2 source lines. 2 labels.