Re: Virtual tape

[CRPence <CRPbottle@xxxxxxxxx>]

  Parallel save to tape is available [from BRMS] to spread save 
activity across multiple [virtual] tape devices.  Two forms of parallel 
save are available; one is a serial format for the data [labels] across 
the different media devices and the other a parallel format where the 
data for the labels is spread across different media devices.  Searching 
tokens PARALLEL SAVE in InfoCenter returns among others, the following link:
http://publib.boulder.ibm.com/infocenter/iseries/v5r4/topic/rzaiu/rzaiusavinglibraries.htm

  If there is not a matching physical drive for each virtual, only the 
serial format is reasonable.  Outside of a utility like BRMS, listing 
the order of the labels to enable consecutive restore would be prudent, 
if fewer physical devices might be available than the number of virtual 
devices used for the save.

  As for storage, the virtual tape device provides no data compaction 
because there is no hardware, but the Data Compression DTACPR() 
parameter enables software compression which can make the saved library 
or object significantly smaller [in its offline size] than its online 
size, but at the cost of the CPU to effect that compression.  The 
offline size for an object is presented in DSPOBJD output.  Other than 
the ability to save multiple libraries on a virtual tape versus only one 
on library into a save file, because the compression is in software, 
there should be little difference between the two.  See the DTACPR 
parameter on SAVLIB for example:
http://publib.boulder.ibm.com/infocenter/iseries/v5r4/topic/cl/savlib.htm

Regards, Chuck

John McKee wrote:
> My question was well answered.  I knew that both virtual tape and 
> save files took up space.  Obviously, for decent performance, a 
> separate ASP is almost mandatory.  What I had wondered was whether 
> multiple processes could be used to speed up backup.  I was thinking 
> that critical libraries could be backed up to a SAVF and later 
> transferred to tape with the system being available for users. Short 
> answer is >maybe<, as availability of DASD is still a factor, as I 
> thought surely it would be.  Years ago, I wrote a CL that prioritized
>  the libraries to be backed up.  Once the high priority libraries
> were safely on tape, other libraries were kept locked and users were 
> allowed back in. As each remaining library was backed up, the lock on
>  the library was released. That did cut downtime considerably, on
> that ancient system.  <<SNIP>>
>
> John McKee wrote:
> > 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?