Re: Raw Devices: Increased Performance?

What about SVM???

Having read this thread with interest (we use raw devices with ptx/SVM), the basic argument is that filesystems are better than raw devices if using OFA because :-

• inodes are not a real overhead because they are in memory and commonly used indirect blocks are cached as filesystem blocks.
• UNIX kernel uses elevator algorithm for data access on filesystems as opposed to the come first served algorithm inherent in raw device I/O.
• In OFA you are spreading the datafiles across the disk bank and so thinning the load on any single controller (on average).

This is comparing UNIX disk / filesystem algorithms versus raw devices as-is.
(i.e. using basic character I/O control)
But in the case of Sequent systems using ptx/SVM is it not a different issue?

Raw device (/dev/rvol/,,,) read and writes go through the ptx/SVM layer which I thought introduced the same kinds of I/O optimizers as the filesystem
(e.g. the elevator algorithm).

It implements striping, and also balances the I/O load between mirrored copies
(i.e. goes to the least busy side of the mirror for read requests).

Is it not the case that raw volumes and raw volumes under SVM are very different in their performance capabilities?
What about a new comparison based on the SVM enhanced raw volume?

The post that spoke of a customer considering Oracle Parallel Server would clearly be referring to a system with SVM, but the arguments being made are not accounting for SVM, just dumb raw devices using basic stream I/O control.

Clarification from a guru requested please ...

Regards, Steve Woolston. (woolsts_at_norwich_union.co.uk) Received on Mon Jul 22 1996 - 00:00:00 CEST