Difference in both Tape and Disk

meenakshi_forum · Active User Joined: 27 May 2008 Posts: 121 Location: India

I would like to know the difference in both Tape and Disk;

advantages of one over another and when each is suggested;

how they work

Thanks.

expat · Posted: Thu Jul 24, 2008 3:38 pm

So here we go down the old 'site specific' route again.

Performance wise, the answer depends on
a) What specific hardware you have installed
b) How much cache your site has purchased for each individual subsystem.
c) How each subsystem has been configured, with taking (b) into account.

Generally speaking, DASD for availability, tape for volume and/or portability.

But then again having work at a few sites with DASD farms of 300+ Tb, DASD was never an issue for virtually any sized file.

gcicchet · Posted: Thu Jul 24, 2008 3:44 pm

Also data on tape cannot be shared, if you have multiple jobs trying to read the data it will be a no goer.

Gerry

dbzTHEdinosauer · Posted: Thu Jul 24, 2008 3:57 pm

tape is more flexible than disk.
fixed disc is the most inflexible.

tape can be repaired, not so easy with a disc.

if you wish to harrass the operations staff, request tapes that don't exist, use multi-reel requests on your jobs to tie up more than one tape drive, request unnecessary (or out of order) tape mounts - that always brings a laugh from the ops-staff. another laugh generator is not specifiying rewind.

As gcicchet said, you can not reserve a disc for only your use, but you can really tie things up with tapes.

gcicchet · Posted: Thu Jul 24, 2008 4:10 pm

Concatenating tape datasets can also be fun, the non use of UNIT=AFF can tie up many tape drives unnecessarily.

Incorrect retention period or expiry dates can exhaust the scratch pool.

Gerry

expat · Posted: Thu Jul 24, 2008 4:48 pm

gcicchet · Posted: Thu Jul 24, 2008 4:51 pm

Writing one 80 byte record to tape is also very popular.

especially if stacking is not available.

Gerry

agkshirsagar · Posted: Thu Jul 24, 2008 5:51 pm

Last few posts should have come with -
CAUTION: DO NOT TRY THIS AT HOME

expat · Posted: Thu Jul 24, 2008 6:03 pm

Garry Carroll · Posted: Fri Jul 25, 2008 1:06 pm

Anuj Dhawan · Posted: Fri Jul 25, 2008 1:32 pm

Hi,

Further,

- DASD is only type of media on which VSAM file can resides
- TAPE file can be accessed in a linear way only
- TAPE drives are not "always in service" of your system, they need to be mounted first
- Usually there is a site-specific limit for the use of max. TAPE-drives in a single JOB, however, it's site specific. At my shop it's 12.
- TAPE drives ar usually used for back-ups
- One can't just browse a TAPE drive, one needs to get file on DASD in order to see the contents of the TAPE file.
- When copying data from TAPE to DASD or vice-versa you might waste a lot of sapce due to the DCB information used; what can happen, to understand this, you can check this link - www.ibmmainframes.com/viewtopic.php?t=23225&highlight=sysut1

Here is a link which tells about different type of TAPE-drives - www-03.ibm.com/systems/storage/tape/drives/index.html

And here is a link for DASDs or Disk drives - www-03.ibm.com/systems/storage/disk/index.html

Anuj Dhawan · Posted: Fri Jul 25, 2008 1:34 pm