[Veritas-bu] Preemptive scheduling

[Joshua Fielden]

Assuming no compression, a slow tape time, and not factoring is tape swap (doing the math on 1 mb/sec less than rated speed should MORE than account for tape swap time), this is ~90G slower than you should get....

[root at peanut  3:39pm] /dev/rmt {519} bc
1024 * 4 * 3600 * 25
368640000

Assuming 5mb/sec (rated for DLT 7k), and compression factors compensate for tape swap time:

1024 * 5 * 3600 * 25
460800000

which is around 180G more than you are getting.

Before the flames of 'lab speed vs real life' come out, let me state that with backups local to the media server, in a previous environment, we were getting (with compression) ~33g/drive/hour. That's three times this speed. Network backups, when tuned right, were getting at least double. This is also with gig pipes, switched FE to the clients, gig on some, etc, etc. I'm working with veritas consulting now to figure out why this 50% speed reduction happens, and will post any tidbits we glean at a later time.

One really helpful link, if you have access to sunsolve is:
http://sunsolve.sun.com/private-cgi/retrieve.pl?doc=infodoc%2F22222&zone_32=netbackup
(sorry, they have much more comprehensive docs than I have been able to find on Veritas' site. If anyone knows where the 'holy grail' of tech note repositories is, please throw a cluon my way)

this is an explaination of how to tune the tape buffers optimally for sun machines and DLT 7k specifically, though it does say it works on other types of high-performance tape technology. Probably a little under-sized if you have DTF 2 drives, though. ;-)
Bear in mind that backups WILL fail if set shmsys:shminfo_shmmax is not set correctly in /etc/system with system errors (undefined) and shared memory errors. This will most likely require a reboot, as the 'default' netb recommended parameter for this is outrageoulsy low for a multi-drive environment. (with our SAN, each media server shares 24 drives, and it's not unheard of for one of the servers to take over 16 or so)

JF

On Tue, Oct 17, 2000 at 03:32:41PM -0700, Richard C Bond filled up my inbox with:
> 
> ?? what/how many tape drives ? I am getting 280 gig in 25 hours, 
> on a DLT 7000. 
> 
> -- 
> -
> Richard Bond (rbond at mbt.washington.edu  (206) 605-3561
> System Administrator                          K-351, Health Sciences Center
> Department of Molecular Biotechnology         Box 357730
> University of Washington                      Seattle, WA 98195
> 

-- 
"Any man page that includes the words "USE AT YOUR OWN RISK. BEWARE OF DOG. 
SLIPPERY WHEN WET" means trouble" - Michael Lucas
Joshua Fielden, Senior Systems Administrator and Backups Team Lead
eXcite at Home, Inc. jfielden at excitecorp.com 650-556-3316