Searching for a faster driver for Compaq's DLT-8000

[mdet]

We are working with a Compaq DLT8000 under AIX 4.3.3 and are experiencing awful performance of this device.
AIX recognises the device as "Other SCSI tape". That might be the reason that only the block_size parameter can be changed and is yielding to a different (not always better) performance. Besides this device is the only one on the SCSI bus.
The only acceptable block size (in matter of performance) is block size "0" (which means variable block size).
Are there any AIX sysadmins who know a trick to boost performance or even have a device specific driver?

 

[bjverzal]

What speeds are you seeing ? You are limited to 6MB native and 12MB compressed with that drive. What model is your server ? What type of SCSI card (feature code 6207 ?)

Thanks, Bill.

 

[mdet]

Hi Bill,
thanks for that immediate reply to my questions.
If you ask "what speeds (we) see..." you probably ask for the real throughput we experience, right?
Well, with fixed block sizes we get something around 100 or 200 kB/sec and with variable block sizes we can boost the device upto 1.4 MB/sec. Not too much, huh? And far away from that "native" 6 MB/sec that is stated in the technical sheets from Compaq.
We are running a rather old (but still going strong) 7012 model G40. We are using an enhanced SCSI-2 fw-diff. adapter (FC 2412). Yes, micro channel.

 

[bjverzal]

Looks like the G40 is a 112MHz CPU, up to 4 of them. Is that correct ?

I have an E30 here (our SP control workstation), and it is a 166MHz machine. Our DLT's top out at about 1.8MB/second on that machine. I suspect you are seeing a machine throughput limitation here. Our 2-way F50 with 1GB of RAM sustains 13MB/second to a new LTO drive though.

I think your server is doing about all it can muster.

Thanks, Bill.

 

[aixqueen]

The aix dlt usually displays as: Perhaps trying to adjust the block size will help?

Default blocksize 1024 See Note 1
Default Density #1 27 ( 70GB )
Default Density #2 26 ( 40GB )

Note 1: I suggest you change the default blocksize from 1024 to 32768 or 51200
if you are using the 'backup' AIX command. Otherwise, backing up with 1024
can be extremely slow
________________________________________________________________

AIX Command Supported Default Block Size RECOMMENDATION

backup 32768 or 51200 Will use either 32768 or 51200
depending on if 'backup' is
by name ( -i ) or not. No
user change is required
tar 10240 There is an error in the manual
that states a 512KB block size.
The user needs to set the
Blocking Parameter to -N64
mksysb See backup mksysb uses the backup command.
No user change is required.

dd n/a The user needs to set the
Blocking Parameter to bs=32K
cpio n/a The user needs to set the
Blocking Parameters to -C64
--------------------------------------------------------

 

[mdet]

I finally got it.
Nevertheless thanks to all contributions.
The Compaq device in fact is a Quantum DLT8000.
I found a description of the recommended and default settings for that tape drive.
Anyone who is interested in, can take a look at

http://www.quantum.com/NR/rdonlyres/0000058fansaemxljpjamlvj/AIX3241Install.pdf

 

[MikeLacey]

mdet -- did you manage to significantly improve the throughput of the tape device? Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.

 

[mdet]

Hi Mike,
the improvement is not as significant as one might wish. The recommended block size (according to Qantum) is "0" which is of no use for dealing with mksysb tapes. Although you can boost the performance by using large block sizes.
Also (with the recommended density_1 and density_2 and block size settings) I was able to write to tape with 2.8 MB/sec

Greetings from sunny (yes, sometimes it happens) Hamburg

(your email account doesn't work so I answer via tek tips).

Michael.

 

[bjverzal]

Block size 0 is OK for mksysb, because mksysb will change it to 512 as needed, then change it back.

BV

 

[mdet]

You're right Bill,
but imagine how long it takes to backup a 10 GB rootvg using "mksysb" if the throughput is about 200 kB/sec.
That's why I can't use it.

Michael.

 

[bjverzal]

Michael,

I definitely know what you are saying. That is about 1/2 the speed of a 4mm DDS-2 tape.

Question - is there any non-rootvg information in your rootvg ? As a practice, I never place anything else but AIX in rootvg.

Thanks, Bill.