I have a question, for some reason cannot read your attachment. Did you
check your performance with raw logical volumes? What kind of throughput
were you getting with them; it would be interesting to know? Or if any one
on the list has any experience with Tivoli, Raw logical Volumes, and LTO1
drives, any input would be appreciated.
Thank You,
Matt Martinez
UNIX Systems Administrator
IDEXX Laboratories, Inc.
Phone:207-856-0656
Fax:207-856-8320
matt AT idexx DOT com
-----Original Message-----
From: Orville Lantto [mailto:orville.lantto AT DATATREND DOT COM]
Sent: Friday, April 23, 2004 5:59 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: TSM and LTO Throughput
This is an account of our experience with TSM and LTO tape drives from
October 2001. I posted some of it on the list back then.
------------------------------------------------------------
I recently was able to experiment on systems with beefy machines, EMC disk,
LTO library, and Fibre. Despite all this hardware, and despite all efforts,
I was unable to get reasonable performance with TSM backing up the file
systems to LTO drives. I tried backing up over the SAN with the Managed
System for SAN client (Storage Agent) and with the standard client to a
local TSM server via shared memory. As the attached table shows, backup
rates for lots of small files is abysmal, 3 MB/sec or less. The backup rate
for larger files was better, but still far below expectations.
Tivoli says that these rates are NORMAL.
Our analysis of this is that the TSM client is unable to send data at a rate
fast enough to keep the LTO drives streaming. This is catastrophic for the
LTO. LTOs are not designed to be speedy when they have to stop, backup, and
index forward, as they have to do when not streaming. To stream an LTO
drive, its tape heads must be fed at 15 MB/sec. With drive compression
turned on, this means that the entire system needs to pass data at up to 75
MB/sec to EACH drive. This is hard to do with most systems, getting disk
systems to move data at that speed is difficult. In addition, there is per
file overhead required for the file system and TSM database. It likely to
be a rare circumstance that will allow LTOs to stream with drive compression
turned on.
------------------------------------------------------------
The lesson is, with LTO-1 technology, the entire data path must support the
streaming speed of the tape drive time the compression ratio or the drives
are MUCH slower. The objects per second rate needs to be low also to
prevent gaps in the streaming of data. I have found few disk systems which
can keep up with a streaming LTO, and then only with large objects (few
objects per second). TSM and the drive microcode have improved, but
upgrading to LTO-2 is the best solution. LTO-2 drives are variable speed
and will throttle down to match your data rate.
Orville L. Lantto
Datatrend Technologies, Inc. (http://www.datatrend.com)
IBM Premier Business Partner
121 Cheshire Lane, Suite 700
Minnetonka, MN 55305
Email: Orville.Lantto AT datatrend DOT com
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