UNIX for Dummies Questions & Answers

Infodoc ID Synopsis Date
13673 ADMIN UFS: how to check what rotational delay and RPM value was set for (newfs -r ) 17 Jun 2002

Description Top

To check what the rotational delay of a disk was set at when newfs'd, do:

/usr/lib/fs/ufs/fstyp -v /dev/rdsk/cXtXdXsX | egrep rps

(where cXtXdXsX is the slice containing the filesystem in question i.e.: c0t0s0s7)

maxcontig 7 rotdelay 0ms rps 90


The formula for calculating rpm is rps*60=rpm.

This disk was newfs'd with a rotational delay of 5400.

i.e.: rps 90 X 60 rpm = 5400

You should see rps 120 if the slice was newfs'd with -r 7200.

Keywords: troubleshooting, ufs

NOTICE:
the above mentioned parameters are obsolete tuning parameters.
These are left over from the days when disk controllers
couldn't read back-to-back blocks done in separate requests
due to lack of buffering. Tuning rpm and rotational delay parameters on today's
drives will cause ufs to interleave which will only slow things down.
Disks/RAID boxes have plenty of buffering these days.

Here are the specifics of what those values do:
The rpm value is only used if rotational delay is also
set to non-zero. If rotational delay is set ("gap" in mkfs),
then ufs will use rpm to determine how many blocks to interleave
when it allocates logically sequential blocks in a file.
This will subvert the ufs "clustering" algorithm that
coalesces adjacent IOs into 1 big IO. This is bad.
Newfs/mkfs default is to disable this stuff.

Also, newfs does not support RPM values of 10,000 or higher.