fast "raw" disk reader utility? (Unix "dd"?)

[Sheldon Smith]

I am looking for a program that will read LBNs (not files) from a specified disk as fast as it can. Does anybody have or know of a port of the Unix "dd" utility to VMS?

(DUMP dd: is way too slow, and
ANALYZE/DISK/READ dd: goes through the file system.)

[Ian Miller. · Accepted solution]

Why do want this?

Does this do what you want
http://h71000.www7.hp.com/freeware/freeware70/diskblock/

[Uwe Zessin]

How about mounting the disk /FOREIGN and then doing a $COPY or $BACKUP/PHYSICAL ?

[Sheldon Smith]

Ian: To make a long story short, to have a throughput test between selected host(s) and selected SAN subsystems. DISKBLOCK is just what I was looking for. Had to encapsulate it to make a command line interface (it's normally an interactive utility).

Uwe: COPY would, except it is not asynchronous. BACKUP/PHYSICAL requires an actual location; can't create a save-set on the "standard" null device.

(If anyone has other ideas, I will still entertain them.)

[Bojan Nemec]

Sheldon,

"BACKUP/PHYSICAL requires an actual location; can't create a save-set on the "standard" null device."

Try with:
$ BACKUP/PHYSICAL dd: NLA0:DUMMY/SAVE_SET

Bojan

[Robert Gezelter]

Sheldon,

A note of caution is in order. To benchmark SAN performance, what you are describing may yield misleading results.

Many controllers have substantial caches, with a variety of settings. The speed of a raw sequential disk copy may be misleading, without a complete analysis of the cache interaction effects. For that matter, many heavy disk writers may benefit from tuning, depending upon the exact behavior of the IO subsystem.

In summary, without supporting work, this may be a misleading benchmark.

- Bob Gezelter, http://www.rlgsc.com