DiskSuite and Prestoserve

Prestoserve^TM is a hardware/software product that speeds response time in disk write-bound applications. The product accelerates performance by selectively caching disk block device write operations in non-volatile memory, reducing disk I/O bottlenecks.

Prestoserve improves NFS^TM server performance, many disk I/O bound applications, and many file systems.

DiskSuite is fully compatible with Prestoserve, with the following restrictions.

DiskSuite Objects Compatible With Prestoserve

• Stripes/concatenations

• Top-level metadevices (mirror is discouraged; see "Why is Using Prestoserve With Mirrors Discouraged?")

DiskSuite Objects Incompatible With Prestoserve

• Underlying component (i.e., submirror)

• State database replicas

• Trans Metadevices (and the underlying master devices and logging devices)

Why is Using Prestoserve With Mirrors Discouraged?

The simple reason is that using Prestoserve together with mirors introduces a single point of failure into the I/O subsystem, which is exactly what mirrors are designed to avoid. The use of Prestoserve lowers the MTBF of a mirror to approximately the same as a single disk.

Why is Using Prestoserve With Trans Metadevices Discouraged?

Prestoserve cannot be used on trans metadevices. Using Prestoserve on a logging UFS can cause system hangs or panics. Prestoserve operates by redirecting I/O from a device to NVRAM. This redirection interferes with the communication protocol between a logging UFS and a metadevice.

How to Configure Prestoserve With DiskSuite (Command Line)

The following steps describe how to load and enable Prestoserve for use with DiskSuite. Basically, you edit the /etc/system file to load Prestoserve after the DiskSuite driver.

1. Add the following line to the /etc/system file.

   exclude: drv/pr

2. Edit the /etc/init.d/lvm.init file and add the following lines to the end of the "start" clause.

   'start') rm -f /tmp/.mdlock if [ -x "$METAINIT" -a -c "$METADEV" ]; then #echo "$METAINIT -r" $METAINIT -r error=$? #echo "$error" case "$error" in 0|1) ;; 66) echo "Insufficient metadevice database replicas located." echo "" echo "Use metadb to delete databases which are broken." echo "Ignore any \"Read-only file system\" error messages." echo "Reboot the system when finished to reload the metadevice database." echo "After reboot, repair any broken database replicas which were deleted." /sbin/sulogin < /dev/console echo "Resuming system initialization. Metadevice database will remain stale." ;; *) echo "Unknown $METAINIT -r failure $error." ;; esac modload /kernel/drv/pr presto -p >/dev/null fi ;;

3. Edit the /etc/init.d/prestoserve file.

   Replace the following line:

   presto -u

   with the line:

   presto -u /filesystem...

   In this command, filesystem... is a list of every file system to be accelerated with Prestoserve. Do not include any of the following:

   • root (/)

   • /usr

   • /usr/kvm

   • /var

   • /var/adm