"Dan Foster" wrote in message
...
In article , Boll Weevil
wrote:

See if you can add this up. To start, we have about 200 Sun servers and
about 1200 NT servers. About 100 Sun servers and about 100 NT servers
are on the SAN and share the following EMC and Hitachi subsystems:

7 EMC 8830 frames with about 13 TB raid 10 useable, each
1 Hitachi 9980V frame with about 45 TB raid 5 useable

There are a whole lot of direct attached SCSI disk arrays and internal
disks in each of the 1200 NT servers. I can't even start as to how much
storage these servers account for. These all get backed up.

Rough calculations shows that using hardware compression for a LTO-2
setup,
one could do all of the above in about 2 (or so) fully decked out IBM 3584
LTO libraries (just as an example), assuming an average size of directly
attached storage for each of the NT servers being 1 TB. A decked-out LTO-2
library with 6 frames should yield in the neighborhood of about 720 TB of
tape storage capabilities.

If 1200 servers * 1 TB = 1200 TB; that'd be one decked out LTO library and
a second library with about 240 TB of available tape space. For the other
stuff... 13 * 7 = 91 plus 45 TB = 136 TB. So you'd still have 104 TB of
free data space, and capable of doing a single full backup for everything
with two libraries and about 3500 tapes.

This assumes 400 GB (hw compressed) LTO-2 tapes; if you are using 20 GB
tapes in uncompressed mode, then your tape requirements goes up by 20
times
3500 for at least 70,000 tapes. Also, if the average per-NT server for
storage is other than 1 TB, that would also influence number of tapes
required, as well.

-Dan

Capacity-wise you're probably correct, I didn't do the math. However, many
of these types of setups have a different limiting factor, being the number
of changes per hour that a tape robot can handle or the number of drives
available. You'd need enough drives to keep the robot busy and a fast enough
robot to keep the drives going. This all depends on the access pattern. If
such a system is used for record based archives then you'll usually need a
lot more exchanges per hour than in a pure backup environment. The fastest
Powderhorns do about 450 exchanges per hour. Just inserting a separate
cartridge for each of the 1400 systems takes 3 hours, assuming one robot and
unlimited drives. Cascading robots help bring this to a lower number.

Also, with this many systems, even if you are doing backup only, you will
run into the issue if the number of parallel tasks you can run. You need a
large number of drives in order to give each system a chance to access one,
or you need to revert to backup software that can combine (multiplex)
several data streams into one.

To make a long story short, capacity is only one factor of many when dealing
with a setup as large as this.

Rob