Managing Serviceguard A.11.20, March 2013

Table 5 Pros and Cons of Volume Managers with Serviceguard (continued)
TradeoffsAdvantagesProduct
No support for RAID 5
• •
•• CVM requires all nodes to have
connectivity to the shared disk groups
Supports activation in different modes on
different nodes at the same time
•• RAID 1+0 mirrored stripes Not currently supported on all versions
of HP-UX
• RAID 0+1 striped mirrors
• CVM versions 4.1 and later support the
Veritas Cluster File System (CFS)
iSCSI Storage and Persistent Reservations
With the A.11.20 PHSS_42558 patch, Serviceguard for HP-UX supports the use of iSCSI storage
with Persistent Reservation (PR) to control access. iSCSI (Internet Small Computer Systems Interface)
is an IP based standard for linking the data storage devices over a network and transferring data
by carrying SCSI commands over IP networks. For information on configuring iSCSI disks, see
HP-UX iSCSI Software Initiator Support Guide available at http://www.hp.com/go/
hpux-networking-docs -> HP-UX iSCSI (SCSI Over TCP/IP) Software. Also, the iSCSI
Software Initiator can be downloaded from software depot at https://h20392.www2.hp.com/
portal/swdepot/displayProductInfo.do?productNumber=T1452A.
Persistent Reservation, defined by the SCSI Primary Commands version 3 (SPC-3) standard, provides
a means to register I/O initiators and specify who can access LUN devices (anyone, all registrants,
only one registrant) and how (read-only, write-only). A PR key (which is an 8 byte value) is used
to register an initiator with an iSCSI LUN and make reservations to gain access.
Multiple initiators can be registered with a given LUN. The LUN maintains a table of pairs where
each entry consists of a key and the corresponding initiator. The combination of the PR keys
registered with the LUN along with the reservation type determine who can access the LUN and
how they can access it.
Unlike exclusive activation for volume groups, which does not prevent unauthorized access to the
underlying LUNs, PR controls access at the LUN level. Registration and reservation information is
stored on the device and enforced by its firmware; this information persists across device resets
and system reboots.
NOTE: Persistent Reservations coexist with, and are independent of, activation protection of
volume groups. You must continue to use exclusive activation feature for LVM and VxVM volume
groups.
Advantages of PR are:
• Consistent behavior.
Whereas different volume managers may implement exclusive activation differently (or not at
all) PR is implemented at the device level and does not depend on volume manager support
for exclusive activation.
• PR prevents stale I/Os coming in anytime on the disks by revoking the access of a crashed
node to stored data and aborting any of its I/Os that are in transit.
For information on features supported by iSCSI LUNs, see “Using iSCSI LUNs as Shared Storage”
(page 32).
iSCSI Storage and Persistent Reservations 89