NetBackup and LTO2 drives - use big blocks!

LTO Ultrium-2 tape drives (at least the IBM ones I have) really, really, really like to see 256KB blocks. Under Veritas NetBackup 4.5FP6, for example, I saw the backup data rates in our environment go from 6MB/sec to 40MB/sec after changing the block size. For the record, we use a Sun 280R with FC-attached LTO2 drives in an L700 library. While I’m not surprised that the default block size used by Veritas wasn’t optimal to get the drives streaming, I was surprised by just how shitty the drives performed with anything but 256KB blocks.

With NetBackup (on a UNIX/Linux server anyways), you’ll have to do some performance tuning to make your fancy LTO2 drives sing. The most important change is to increase the data buffer size (Veritas-speak for “block size”) and increase the number of these data buffers. This is only necessary on the media manager host (since it talks to the tape drive).

# echo "262144" > /usr/openv/netbackup/db/config/SIZE_DATA_BUFFERS
# echo "16" > /usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS

On a Solaris server, the increased buffer sizes will almost certainly cause NetBackup to exhaust the available shared memory…. This is one of those weird Solaris-ism’s where Sun still uses rediculously small default limits on the shared memory and IPC subsystems. So we have to update the hard limits built into the kernel at boot time by modifying /etc/system. Since we’re in there, we’d might as well up the limits on all the little bits we’re likely to bump into:

set msgsys:msginfo_msgmni=1024
set msgsys:msginfo_msgtql=1024
set semsys:seminfo_semmni=2048
set semsys:seminfo_semmns=2048
set semsys:seminfo_semopm=128
set shmsys:shminfo_shmmax=33554432
set shmsys:shminfo_shmmni=512

Note:These tunables are strictly for Solaris 9. Solaris 7 and 8 have slightly different sets of tunables that must be adjusted in /etc/system. Tech Note 264967 talks specifically about these Solaris 9 tunables. See Tech Note 240733 - NetBackup Performance Tuning Guide for UNIX Platforms for more generic performance tuning of NetBackup, including some good tips on indexing the image catalog and older versions of Solaris.