Date: Thu, 17 Oct 2002 21:55:40 -0700 From: Mike Thompson <mike@atomz.com> To: freebsd-scsi@FreeBSD.ORG Subject: Multiple FreeBSD SCSI Hosts Message-ID: <4.3.2.7.2.20021017212517.00aede00@pop.atomz.com>
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I'm interested in setting up two FreeBSD systems in a very simple
clustering type configuration around centralized external SCSI storage
devices for hardware redundancy. The specific configuration I'm thinking
about is shown in the simple diagram below:
+-----------+ +----------+ +-----------+
| FreeBSD | | | | FreeBSD |
| Host 1 | | External | | Host 2 |
| (primary) | | SCSI | |(secondary)|
| | |RAID/DRIVE| | |
| SCSI r/w | | | | SCSI r/o |
+-----+-----+ +---+--+---+ +-----+-----+
| | | |
+---------------+ +---------------+
There would be two FreeBSD systems with the primary server mounting the
external SCSI storage read-write and the secondary server mounting the
external SCSI storage read-only. Each server would have non-shared /, /usr
and /var partitions on local drives. In a fail over situation, I would
manually power down the primary server and re-mount the SCSI storage
read-write on the secondary server to continue operation. My questions
about this are as follows:
1. Do the FreeBSD SCSI drivers support such a configuration by implementing
the SCSI RESERVE/RELEASE commands to lock access to the SCSI bus? If so,
which drivers for which specific SCSI adapters?
2. Many external raid controllers describe themselves as host dual
capability. Is the type of configuration they are describing?
3. Will the secondary server still experience a corrupted file system
because of write caching by the primary server? If so, would it be
possible to configure the primary server to write through the cache?
4. Are there any FreeBSD specific projects or ports that would make such a
dual host SCSI configuration easier to configure or maintain?
5. What am I overlooking in such a configuration?
6. Are there alternatives to this type of scenario that may work better for
FreeBSD?
7. Finally, are there resources already on the web that would answer these
questions for me?
I would be very much interested in hearing if other people have attempted
such a configuration with FreeBSD servers and their experience. Also,
specific hardware recommendations would be helpful.
Thanks,
Mike Thompson
mike@atomz.com
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