In the Cluster Edition, database devices—except those private devices that are used by local user temporary databases—must be raw devices (also known as character devices). You cannot use block devices as database devices because they can buffer disk writes at individual hardware nodes, causing data inconsistency among cluster instances.
You can create private devices on block devices. Private devices are used only by local user temporary databases. See your operating system documentation for more information about configuring raw devices.
You can create local user temporary databases on private devices, but you must create local system temporary databases on shared devices. For the Cluster Edition, you can use less expensive, local file system devices (block devices) for managing the storage needs of temporary data in the cluster. These devices are added as private devices and can only be used by local user temporary databases. See Chapter 8, “Using Temporary Databases.”
For example, on Linux systems the path /dev/sda is a block device and should not be used. However you can bind this block device to a raw device such as /dev/raw/raw1.
On Linux systems, you can distinguish character (raw) devices
with the file type displayed using the command. Block devices include
a b as the file type and
character (raw) devices have a c as
the file type:
[joeadminitrator@isles ~]$ ls -l /dev/sda brw-rw---- 1 root disk 8, 0 Nov 29 06:15 /dev/sda [joeadministrator@isles ~]$ ls -l /dev/raw/raw1 crw------- 1 sybase sybase 162, 1 Nov 29 12:17 /dev/raw/raw1
On Solaris systems, the path /dev/dsk/c0t0d0s1 is
a block device and should not be used. However, you can access this
same storage as a character device with the path /dev/rdsk/c0t0d0s1.
Using an ls -l command on the character device indicates raw at
the end of the symbolic link:
janeadministator% ls -l /dev/dsk/c0t0d0s1 lrwxrwxrwx 1 root root 49 Apr 23 2007 /dev/dsk/c0t0d0s1 -> ../../devices/pci@780/pci@0/pci@9/scsi@0/sd@0,0:b janeadministrator% ls -l /dev/rdsk/c0t0d0s1 lrwxrwxrwx 1 root root 53 Apr 23 2007 /dev/rdsk/c0t0d0s1 -> ../../devices/pci@780/pci@0/pci@9/scsi@0/sd@0,0:b,raw
On HP Itanium systems, the path /dev/disk/disk4 is
a block device and should not be used. However, you can access this
storage as a character device with the path /dev/rdisk/disk4.
You can distinguish character (raw) devices with the file type displayed
using the ls -l command. Block devices include
a b as the file type and
character (raw) devices have a c as
the file type:
[jphui@hpiastr1-HP-UX]:/> ls -l /dev/disk/disk4 brw-r----- 1 bin sys 3 0x000000 Feb 23 11:40 /dev/disk/disk4 [jphui@hpiastr1-HP-UX]:/> ls -l /dev/rdisk/disk4 crw-rw-rw- 1 bin sys 23 0x000000 Feb 23 11:40 /dev/rdisk/disk4
On IBM AIX systems, you can distinguish character (raw) devices
with the file type displayed using the ls -l command.
Block devices include a b as
the file type and character (raw) devices have a c as
the file type. The path /dev/hdisk1 is
a block device and should not be used. However, you can access this
same storage as a character device with the path /dev/rhdisk1:
janeadministator% ls -l /dev/hdisk1 brwxrwxrwx 1 root root 49 Apr 23 2007 /dev/hdisk1 janeadministrator% ls -l /dev/rhdisk1 crwxrwxrwx 1 root root 53 Apr 23 2007 /dev/rhdisk1
Database devices in the Cluster Edition must support SCSI-3 persistent group reservations (SCSI PGRs). The Cluster Edition uses SCSI PGRs to guarantee data consistency during cluster membership changes. Sybase® cannot guarantee data consistency on disk subsystems that do not support SCSI PGRs (Sybase does support this configuration for test and development environments where data corruption is tolerated).
PGRs are a feature of the SCSI-3 protocol. However many storage area networks (SANs) that employ less expensive SATA disks still provide this functionality. Contact your storage vendor to verify your system supports SCSI-3 Persistent Group Reservation.
See the installation guide for your platform for additional information about devices and I/O fencing.
I/O fencing is not supported on Solaris non-global
zones.
