One of the things I've wondered about VTL's and file devices is how they
handle seeks.
What happens when TSM needs to access a file that's at the end of a vtl
"tape" or file volume?
For a file device, does TSM open the file and read the entire volume till
it gets to the
file or is tsm smart enough to seek closer to the file. If it has to read
the entire volume then this is an
argument for smaller file volumes.
For a vtl - same basic question. Since a vtl emulates tape drives, I
assume tape marks
have to be recorded. I wonder if a vtl indexes the tape marks so it can
seek directly to a mark
on disk.
Rick
"Loon, E.J. van -
SPLXM" To: ADSM-L AT VM.MARIST
DOT EDU
<Eric-van.Loon@KL cc:
M.COM> Subject: Re: File dev. type vs.
VTL
Sent by: "ADSM:
Dist Stor
Manager"
<[email protected]
.EDU>
06/20/2005 06:56
AM
Please respond to
"ADSM: Dist Stor
Manager"
Hi Dough!
We choose a VTL over a file device class because several reasons:
1) IBM couldn't provide us a reference site with a 100 TB. + file device
class.
2) We were not sure how AIX would handle a crash with several very large
filespaces. How long will a filesystem check last?
3) How long will it take for TSM to mount a few hundred file volumes during
startup?
If you decide to use a file device class, limit the size of your volumes
and
pre-define them. The smaller the volumes are, the less volume contention
you
will encounter during multiple (multi-session) restores. You should
pre-define them to prevent fragmentation on the disks.
Kindest regards,
Eric van Loon
KLM Royal Dutch Airlines
-----Original Message-----
From: Thorneycroft, Doug [mailto:dthorneycroft AT LACSD DOT ORG]
Sent: Friday, June 17, 2005 19:47
To: ADSM-L AT VM.MARIST DOT EDU
Subject: File dev. type vs. VTL
I'm getting ready to add more disk to my TSM server,
Are there any advatage/disadvatages to using a Virtual tape library
instead of TSM defined file device types.
(Do TSM file device types work with multi session restores?)
Doug Thorneycroft
> Systems Analyst
> County Sanitation Districts of Los Angeles County
> 1955 Workman Mill Road
> Whittier, CA 90601
> Tel: (562)699-7411, Ext. 1058
> Fax:(562)695-6756
> www.lacsd.org
>
>
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