HP StorageWorks Scalable File Share System Installation and Upgrade Guide Version 2.2

Configuring the storage5–4
is used to store data. Replace the failed disk as soon as possible, because a subsequent disk failure
may cause you to lose access to data.
• The total size of the LUNs in a disk group must occupy less than 90% of the available capacity of the
disk group. This limit applies to the actual capacity of the disk group, not the raw capacity of the
disks in the disk group. The actual capacity is much lower than the raw size of the disks due to disk
sparing. The redundancy overhead further reduces the actual capacity. The size of the LUN is
specified when the virtual disk is created using the ADD VDISK command.
• LUNs must use RAID5 redundancy level.
• Each LUN must be presented to the HBA ports of both servers in a server pair. (The servers in a server
pair are capable of taking over services from each other.)
• The maximum supported LUN size on an EVA4000 array is 2TB.
Examples of implementing these rules are discussed later in this chapter.
5.1.3 Assigning and sizing LUNs on EVA4000 storage
The information in this section is organized as follows:
• Assigning and sizing LUNs on EVA4000 storage — overview (Section 5.1.3.1)
• Assigning and sizing LUNs on EVA4000 storage — examples (Section 5.1.3.2)
Plan your LUN configuration according to the guidelines described in this section. Use the worksheets in
Table B-8 and Table B-9 (one copy of this worksheet for each array) in Appendix B to record the details of
your storage configuration, including a mapping of the LUNs that will be on each array, and the arrays that
will be connected to each server pair. (You can add the WWIDs of the arrays, LUNs, and HBA ports to the
worksheets at a later time.)
5.1.3.1 Assigning and sizing LUNs on EVA4000 storage — overview
This section describes the virtual disks you must create for use as LUNs within the HP SFS system, their size
and their purpose.
The primary purpose of the EVA4000 arrays is to store the Lustre file system data. However, the HP SFS
system also uses some storage to manage the system. When you configure the system, you use LUNs for
each of these different purposes, as follows:
MDS LUN
MDS LUNs are used to store the meta-data for a Lustre file system. In the HP SFS system, you must
create two MDS LUNs for each file system you intend to create. Each of the two MDS LUNs
stores a copy of the file system meta-data; this allows for disaster recovery of the meta-data in
the event of multiple simultaneous disk failures resulting in the loss of a single disk group on an
EVA4000 array.
The two MDS LUNs must be created on an EVA4000 array that is connected to the MDS and
administration servers, and must be in different disk groups.
In the HP SFS user interface, an MDS LUN is identified as an mds LUN.
OST LUN
OST LUNs are used to store object data (that is, file contents) for a Lustre file system. The number
of virtual disks that are created for use as OST LUNs depends on the number of EVA4000 arrays
in your system and on the number of file systems you plan to create. Two virtual disks are created
for use as OST LUNs on each array, with each of the LUNs created in a different disk group.
Both of the LUNs on the array must be allocated to the same file system.
In the HP SFS user interface, an OST LUN is identified as an ost LUN.