[Networker] Best way to evaluate drive speed?

I think I'm asking too many questions here, but it's related so ...

How do we best determine if we're getting reasonable write speed on ourtape drives?

We have 4 SDLT 600 drives in a LVD Quantum library attached to a Linuxstorage node. We're using SCSI interface with dual channel host adaptercards (LSI 22320 Ultra320) which supplies 160 MB/channel. Drive1-2 aredaisy chained to channel A. Drives 3-4 are daisy chained to channel B.Perhaps each drive should be on its own channel, but given the speed ofthe channel it seemed OK to have two drives share a channel. Was notgoing to have more than 2 drive per channel, however. But, bursttransfer speed does list as 160 max, so with two drives that would be320 so maybe they should each be on separate channels. Anyway, theproduct information indicates that these drives have a speed of 35native, 70 MB/sec with compression. I assume this is a best casescenario, and I doubt we'll be able to match those in practice, and itmight make a difference if the data is local to the snode or coming overthe network, but how do we determine if we're getting good results?


This brings up 3 questions:

1. What are the vendors doing to claim these numbers? How are theywriting the data during the tests so as to optimize the speed to claimthe best possible results?

2. What is a good way to determine if the drives in your library arefunctioning at their proper speeds?

3. Does sending more save sets to a tape device really increase thespeed, and if so, why? I thought I've seen this behavior before whereinthe speed increases (to a point) when more sessions are running, butmaybe that was coincidental. I mean, why would one large save set (as inone large enough such that when you're doing a full, it will take awhile so there's no shoe shining effect and the drive can just streamalong) not do the same as multi sessions?

I was thinking to first run some non-Legato tests by tarring a 2 GBdirectory on the storage node directly to one of the devices, time theoperation and then do the math. Perform a tar extract to ensure itworked correctly. I don't think I can run multiple concurrent tarsessions to the same device, though, like multi-plexing in NetWorker.Will this still yield a good idea of the drives speed? Not sure thiswould fill the buffer fast enough or generate good enough burst speedlike if I'm running multiple save sets in NetWorker, but I refer toquestion 2. above?

If sending more sessions to the device does increase the speed then whenusing NetWorker to send multiple sessions to the device, so as to betterfill the buffer and increase drive speed, how can I best capture theresults? Is it obvious enough to simply create a group, place the snodein the group, specify 'All' for the client's save sets and then justlaunch a full and then look at the start and completion times for thegroup and how much total was backed up and do the math to get an averagedrive speed? There are 5 file systems on the snode, and 4 are very small(under 300 MB) except for /usr which is about 6 GB, so we all know whichone will still be cranking on a full long after the others are done.Will this be a fair test? Maybe better to create say 4 separate namedpaths of 1 GB each, for example, and list those as the save sets? Again,this gets back to question 2. above.


Thanks.

George


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