Andy Raibeck wrote:
>Here's a feature that I'd *love* to see put into ADSM: the ability for ADSM
>to pre-stage tape mounts, especially for restore. Here's how it would work:
>
>1) A restore that will require multiple tape mounts is started.
>
>2) ADSM calls for the first n tapes to be mounted. 'n' is defined by an
>   ADSM server option called PRESTAGE (I'm making this up). The default
>   value for 'n' is '1', which is what we have today. 'n' is limited only
>   by the number of available tape drives.
>
>3) As each tape is mounted, ADSM positions it to the first location from
>   where data will be read. While the first tape is actually being read,
>   the second, third, and so on are mounted, positioned, and ready to be
>   read.
>
>4) After the first tape has been read, ADSM can immediately start reading
>   the second tape. The first tape is dismounted, and the nth + 1 tape is
>   called for.
>
Why would ADSM have to wait until the first tape is read before reading
tapes 2,3 etc.? Theoretically it should be possible to read all tapes
simultaneously, although the implementation may be more difficult. Is there
something I am overlooking?

>This should work because ADSM already knows what tapes will be called for
>(this must be true because ADSM sorts the list of versions to be restored
>by volume).
>
>Such an implementation would speed recovery by almost eliminating the lag
>time between tape mount and locate. This would provide the restore
>performance benefits of collocation+ without having to incur the overhead
>of collocating the data. The actual number of tape mounts would not be
>reduced, just the lag time between one tape and the next.
>
>Any comments/thoughts?
>
>Andy Raibeck
>Connecticut Mutual
>203-987-3521
>
>
Rob Creecy
Census Bureau
DIR IT, 1029-3
Washington, D.C. 20233

(301)-457-1774    rcreecy AT census DOT gov