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Conference ssag::ask_ssag

Title:	Ask the Storage Architecture Group
Notice:	Check out our web page at http://www-starch.shr.dec.com
Moderator:	SSAG::TERZAN

Created:	Wed Oct 15 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	6756
Total number of notes:	25276

6509.0. "TZ88 write perf., NT3.51 SP4" by RTOMS::dhcp-203-80-56.suo.dec.com::Wagenblast (This brain intentionally left blank) Tue Mar 25 1997 00:38

I am currently doing a benchmark on an AlphaServer 4100. We have six TZ88s 
on three KZPSAs (using DWZZXs into the storage shelf). Windows NT 3.51 SP4. 
TZ88 driver from www.windows.digital.com.

With NT Backup the maximum write performance we get is 1.5 Mbyte/s. 
Sometimes less. In NT Backup we specify "hardware compression enabled". 
Also the compression light on the drive is on, maximum density is indicated 
on the drive. We use CompacTape IV. 

Any idea what we could do wrong? Theoretically write performance should be 
between 1.5 and 3.0 Mbyte/s depending on compression, and not between 1.0 
and 1.5 as we get it, right?

Thanks for any insight,
Thomas Wagenblast

T.R	Title	User	Personal Name	Date	Lines
6509.1	Hmmm...	SUBSYS::alcor.shr.dec.com::smith	Apps Engineer	`Tue Mar 25 1997 07:37`	12
	Hi Thomas, It's been a long time since we've spoken! The drive is rated at 3MB/sec. assuming 2x1 compression. Depending on what type of data you are backing up, you may not get ANY compression, and in RARE circumstances, you can get NEGATIVE compression (yep it'll expand!). What type of data are you backing up? Joe Smith
6509.2		TAPE::PETERS		`Tue Mar 25 1997 07:44`	10
	What does the Disk subsystem look like ? What host controller ? What type of disk ? Single disk or raid ? Steve P.
6509.3	will do some testing with PS file	RTOMS::dhcp-203-80-56.suo.dec.com::Wagenblast	This brain intentionally left blank	`Wed Mar 26 1997 09:09`	17
	We backup quite a range of data..... when backing up a NT3.51 system disk we get exactly 1.5 Mbyte/s. The system disk is a RZ29, connected to a KZPDA. Other disk with page file on the same controller. But during the backup no paging occurs. Other stuff we backup are for example Oracle export files. Maybe just for test purposes I should get some large crap Postscript file, replicate it 100 times and measure the time for the backup of that. If THIS does not compress, nothing will compress, right? Any newer insight is welcome, otherwise I'll do the test above and post my findings here. Thomas (Hi Joe, greetings to Cathy!!!)
6509.4	Could be the KZPDA...	SUBSYS::alcor.shr.dec.com::smith	Apps Engineer	`Wed Mar 26 1997 09:34`	5
	I don't have any details, but I remember someone saying that disk reads on the KZPDA are very bad... Can anyone corroborate/discount this? Joe
6509.5	ok now	RTOMS::dhcp-203-80-56.suo.dec.com::Wagenblast	This brain intentionally left blank	`Mon Apr 14 1997 01:42`	10
	Did some measurements myself, everything fine now. Customer did first measurements, and mixed up compressed/uncompressed transfer rates. Now I got a fine 1.5 MByte/s uncompressed, backing up 1000 vanilla Postscript files I got a compression ratio of 2.4. Re.4: Yes, KZPDAs are VERY bad if you put more than one per PCI bus into the system. I fell into that pit once.... Thomas