If you need to extend its size in
the future, make up a new group of disks into a RAID-5 array and extend
the filesystem onto it. It is possible to grow a filesystem on-line if
necessary, so there is no need to rebuild the whole array and restore
it from backup tapes. Each RAID-5 array should contain between 5 and 30
disks. I've used a 25-disk, RAID-5 setup on a SPARCstorage
Array. For highest performance, keep it to the lower end of this range,
and concatenate more smaller arrays together. We have found that a
128-kilobyte interlace is optimal for this largely random access workload.
Another issue to consider is the filesystem check required on
reboot. If the system shut down cleanly,
fsck can tell
it is safe to skip the check. If it went down in a power outage or
crash, it could take tens of minutes to more than an hour to check a
really huge filesystem. The solution is to use a logging filesystem,
where a separate disk stores all the changes. On reboot,
fsck just reads the log in a few seconds and it is done.
With Solstice Disk Suite (SDS), this is set up using a "metatrans"
device, and the normal UFS filesystem. In fact, an existing SDS
hosted filesystem can have the metatrans log added without any
disruption to the data. With the Veritas Volume Manager, it is necessary
to use the Veritas filesystem, VxFS, as the logging hooks in UFS are
For good performance, the log should live on a dedicated disk. For
resilience, the log should be mirrored. In extreme cases, the log disk
might saturate and require striping over more than one disk. In low
usage cases, the log can be situated in a small partition at the start
of a data disk.
An example result is shown below. To extend the capacity, you would
make up another array of disks and concatenate it. There is nothing to
prevent you making each array a different size either.