Re: [Networker] Slightly off-topic query
2006-07-21 09:35:41
We've used FC-SCSI bridges for many years now with no issues. In fact,
the library we use for NDMP has two of them in it (added a second last
week).
To make it simple, t's all about bandwidth. We look at the total, native
bandwidth of our backup devices then multiply that by the typical
compression that we see. This gives us a decent approximation of how much
data the drives can handle. We then add in 10% - 20% extra (after
compression for a safety net.
Let's say I just have one LTO2 drive doing Windows backups: 30MB/sec
native * 1.5 compression = 45MB/sec; add 6.75 MB for safety net (round to
7MB) and we have 52MB/sec that I need to push to this drive. If this
drive is doing Oracle, I would have (30MB/sec * 3 compression) = 90MB/sec;
add 15 MB for safety net and we have 105MB/sec. Does that seem high for a
30MB/sec device? Absolutely. Remember that the native drive speed is the
fastest that the heads can put data onto the media - period. At 3:1
compression, I need to push 90MB of data to keep the drive at 30MB =).
Using my target numbers I can then look at my connectivity to see the best
way to lay things out. We've found that the trick with FC-SCSI bridges is
not forgetting to take the SCSI portion of it into account when planning
for throughput. Just because you have 2Gb FC coming in, doesn't mean
you'll be able to push that through SCSI on the other end. This is
especially true when mixing drive types as the entire SCSI channel will
drop to the speed of the slowest device.
I would also recommend dedicating one FC card/port for tape and a second
one for disk. This is a best practice (requirement?) with Sun servers.
It's especially recommended if you're backing up those disks to tapes on
the same system - data in from disk doesn't have to fight data out to
tape.
If this data is coming in over the network, don't forget to factor that
bandwidth in as well. To push 200MB/sec to your tape devices (a single
2Gb FC), you have to be able to pull that through the front end (2x GbE).
The new 4Gb FC means 4 x GbE.
Finally, be sure this 1U server has the horsepower to move all this data.
They don't in our environment so we have to use 4 CPU systems.
I hope that helps...
Jeff Mery - MCSE, MCP
National Instruments
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Olaf Zaplinski <o.zaplinski AT BROADNET DOT DE>
Sent by: Legato NetWorker discussion <NETWORKER AT LISTSERV.TEMPLE DOT EDU>
07/21/2006 06:32 AM
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Olaf Zaplinski <o.zaplinski AT BROADNET DOT DE>
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Re: [Networker] Slightly off-topic query
Hmm, we are thinking of replacing our old server that has several SCSI
HBAs
attached to one LTO2, three LTO1, two disk devices and the library. Could
we
buy a SCSI/FC bridge, attach all SCSI devices to it and buy a small 1HE
server with one FC HBA? Would that work, or would we get performance
issues?
Olaf
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