ADSM considerations aside, from a hardware view in this environment SCSI is
definitely the way to go. Not only is SCSI superior handling multiple
simultaneous accesses, it is much less CPU intensive. When a SCSI drive is
accessing, it normally uses 10-20% of the CPU, where IDE can use between
70-90%. That's why on a desktop system using IDE, when you transfer large
amounts of data (such as copy one drive to another) the system becomes
extremely sluggish during the transfer. SCSI will not normally have this
impact. IDE may have evolved to surpass SCSI in some aspects, but SCSI is
still the only choice in a server/multi-access environment.
Roger C Cook
RCG Information Services
Hi,
Recently, we're trying to decide about the various ways in which TSM can be
set up. We need about 2Tb of primary pool space. For primary pool only , we
may either:
1) Get a big library, and a lot of tapes, amounts to >$50.000. (With the lib
we can also maintain the copy pool)
2) Get a bunch of IDE-disk cabinets, and a lot of 70 Gb IDE disks, amounts
to $25.000 or so (of course we will also need a small library for the copy
pool). These cabinets have a scsi interface.
It seems IDE disks are not only the cheaper, but also the much faster
solution for daily retrieve operations. In this case we would opt for a
RAID-5 IDE set for primary stg (but also a fast(er) SCSI system for the DB
and LOG). With this amount of disks some are bound to crash every now and
then, RAID-5 helps. All in all, the TSM server only 'sees' scsi.
One cabinet would show up like one disk, in reality 70Gb disk times 7 disks
= 0.5 Tb/cabinet, which is a rather big 'disk' size.
Question 1) However, on the forum no-one seems to use a PRimary IDE (PRIDE)
disk pool? Why? I'm i missing something or what?
Question 2) If PRIDE seems like a good solution, would the better way to use
DISK devices (any TSM limits?, caused by size or sheer number of DISK
volumes on the PRIDE disk) or FILE devices (but fragmenting files all over
the disks, and need of reclaim)
Question 3) Any (other) TSM limits endangering this plan (we are talking
about 2Tb or more on disk...)
Of course OS limits have been accounted for. It seems AIX and NT are OK.
Thank you,
Allshare Personnel BV
Jochem van Hal
TSM admin
jvhal AT allshare DOT nl
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