Thanks for everyone's responses.  I posted this same question to another
listserv and from the two got a wide range of opinion back.

As summary:
1) Is it wise to mix disk and tape on the same SAN?
**) It is OK to share a fabric with tape and disk targets.  Depending on the
devices you may however need to zone devices to prevent conflicts - but this
is also true of different host types / HBA manufactures / disk subsystems.
**) Sometimes from a cost perspective it is better to use different switches
for disk and tape.  Likely your switch ports for disk are high performance /
high availability and sometimes you can do with less caliber switch ports
(and hence cheaper) for tape.

2) Can the HBAs in our hosts be used for both disk and tape access?
**) Officially you will find it very difficult to find a vendor who will
suggest sharing HBAs.  Some vendors explicitly recommend not sharing (IBM
for example in their Ultrium device drivers guide), but nothing I've seen
goes so far as to say "unsupported", and nothing has said that it flat out
won't work.
**) Unofficially many people share the HBAs for both disk and tape without
any problems
**) Be cognizant of performance aspects as they may push you away from
sharing anyway
**) One person commented that a couple of years ago he encountered a
situation where problems with a tape device caused his tape HBA to lock up
in its entirety.  If shared for disk that could be more catastrophic....

Lots of opinions but the real choices are left to the those implementing!

Cheers,
-Chris
----- Original Message -----
From: "Chris Madden" <maddenca AT myrealbox DOT com>
To: "Legato NetWorker discussion" <NETWORKER AT LISTMAIL.TEMPLE DOT EDU>
Sent: Tuesday, April 08, 2003 6:17 PM
Subject: SAN Tape Drive / Storage / Host Connectivity


> I have a SAN in production for disk access and we are looking at adding
> fibre tape drives to the setup, initially driving these devices from a
> single storage node and thereafter doing LAN-free backups (i.e. installing
> additional storage nodes) on some larger hosts over time.  Today I have 2
> distinct SANs which are mirror copies of each other for availability, and
> have zoning implemented so that only hosts of a given OS type can see each
> other and their storage ports.  Tech environment includes: IBM ESSs, AIX,
> Solaris, Win2k, Netware, and coming soon 6 x IBM 3590H and 6 x IBM LTO-2
> drives.
>
> In order to add tape devices to the SAN I have some questions:
>
> 1) Is it wise to mix disk and tape on the same SAN?  My initial reaction
is
> why not if you zone correctly, but perhaps there are other issues?
>
> 2) Can the HBAs in our hosts be used for both disk and tape access?
Again,
> my initial reaction is why not but perhaps there are other issues?  Is the
> answer different for each OS and if so which are OK and which not?
>
> I would prefer to share as much infrastructure between disk and tape as
> possible and I suspect with proper zoning the same fabric can be used for
> tape and disk.  If the case is however that I can't share the existing
HBAs
> and need to add a 3rd HBA for tape use I have to pick which SAN (A or B)
to
> plug it into, or I have to add a 4th HBA to get visibility to all the
> drives.  At that point the complexity (i.e some drives/hosts on one SAN
and
> some on the other) suggests leaving SAN A and SAN B in place for disk, and
> creating a SAN C for tapes.  Creating SAN C however has significant costs
> (more switches, more HBAs) and would need good justification.
>
> Fellow NetWorkers, what would you do in my shoes?
>
> Kind Regards,
> Chris
>
>
>

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