Ok here comes the big "It Depends"

Some VTL's offer data compression. Some use 1GB Ethernet and other are
2, 4, 8 GB fiber. Writing to a save file in the same ASP can be slow do
to the fact you are using the same disk you are backing up to backup to.
Separate ASP is faster than tape and possible faster than VTL if you
have enough arms in the secondary ASP. I am still searching for that
shop that is using a VTL. IBM storage says that VTL are slower than
tape. I find that hard to believe. IBM also says that you cannot use a
VTL as an alternate IPL device. I still find that hard to believe as
the VTL should look just like a tape device on the iSeries. Wish I had
a real world expert on iSeries and VTL to answer my questions.



Chris Bipes
Director of Information Services
CrossCheck, Inc.


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of John McKee
Sent: Wednesday, September 03, 2008 11:45 AM
To: Midrange Systems Technical Discussion
Subject: Virtual tape

To back up 100G of DASD to virtual tape, would you need 100G of DASD for
the virtual tape? Or possibly a better question: Does virtual tape
utilize data compression, thus not requiring quite as much space as if
data was simply copied disk to disk?

How would the size be calculated?

How does virtual tape compare to using a save file or multiple save
files?

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