Hello,
My many thanks for everyone's response!
ORIGINAL QUESTION:
------------------
> Can anyone explain how splitting up a disk between multiple domains
> (in Advfs) can degrade performance?
SUMMARY:
--------
Other than the obvious performance degredation one might see when
users access files from different domains, located on the same
disk, at the same time, the following best explains what also
occurs.
In the words of Alan from Dec:
AdvFS is a log based file system; all metadata changes to
the file system are written as a journal to the log space
of the file system as sequential writes. As the log becomes
full the changes are merge back to the file system. On a
typical domain, the perfect I/O load is one which does nothing
but sequential writes to the log (changes metadata).
With two domains on the same disk you'll have two logs and
this will cause seeking between the two logs even if the
load is ideal for each domain. Seeking slows down disk
access time, which degrades performance. Left to itself
AdvFS seems to allocate data close to the location of the
log which keeps down the seek distance even when the
load is random. With two domains, you're seeking across
much of the disk from one domain to the other.
Solution - Get a pair of solid state disks, mirror them and
put the logs for both domains on a partition of each. They'll
have exception seek times and you'll only need to worry about
the non-log seeking for doing I/O on the two domains.
Thanks again,
Bill Antoniadis
Received on Thu Oct 01 1998 - 15:22:21 NZST