I resisted including this, because only one session can actually write to
the volume, but many can read from it.  This is mainly for restore
performance.
It still doesn't address the queueing issue.  For sequential files,
multi-session write access would introduce multi-plexed data streams.  I
much prefer migration from random access disk if the alternative is
long-term storage in a multi-plexed format.  (bad netbackup memories)

Backing up directly to sequential devices makes sense for large
files/nodes.  However, we have hundreds of machines that only back up a
few GB per night.  Random access disk is best for this.  The "Max size
threshold"  is ideal for controlling this.

I really believe the disk and file devices are complements and not
competitors.  I bet IBM is developing file devices heavily because it is
relatively new and not mature. I don't believe they are trying to supplant
disk devices. The real file-device competitor is VTL and those are the
features that IBM is pursuing (deduplication, etc)
I don't think random-access disk is going anywhere.

Regards,
Shawn
________________________________________________
Shawn Drew





Internet
tsm AT NETWORKC.CO DOT UK

Sent by: ADSM-L AT VM.MARIST DOT EDU
09/21/2009 11:51 AM
Please respond to
ADSM-L AT VM.MARIST DOT EDU


To
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Subject
Re: [ADSM-L] the purpose of "file" device class






Just to be uber-picky, FILE volumes now do allow multiple
sessions/processes
to read/write concurrently to a single FILE volume from TSM 5.5 onwards
(
http://publib.boulder.ibm.com/infocenter/tivihelp/v1r1/topic/com.ibm.itsmms

munn.doc/anrsgd5515.htm#wq28).

The big picture as I've read it is that IBM are perhaps angling the
user-base towards using FILE volumes, and that new developments would be
implemented against FILE technology rather than DISK. That being said,
it's
fair to say that many people are simply more comfortable with the ease,
simplicity and habit of implementing and managing DISK volumes.

/DMc

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Shawn Drew
Sent: 21 September 2009 15:58
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] the purpose of "file" device class

Disk Based (Random access) lets you have several sessions all sending data
to it.  This removes the need to queue backups like all the competitors.
But it will fragment as data expires and there is no defrag for random
access.

File devices (Sequential access) do also fragment over time, just like
tape, but you are able to run reclamation on them.  But sequential access
would cause queuing.
They each have different pro's and con's which make them suited for
different tasks.  (long term vs short term storage)

Regards,
Shawn
________________________________________________
Shawn Drew


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