I'm looking for feedback from anyone else who has been using a VXA 
drive on a Mac with Retro 4.2. We are currently evaluating the VXA 
drive in the internal configuration on the Fast SCSI-2 bus in a Power 
Tower Pro 225 and have been seeing very mediocre throughput when 
compared to the existing DDS-2 drive on the external slow SCSI bus.

Here are the results of some testing I did:

>So I did some testing: I created a 25 MB disk image file (single 25 
>MB file, all zeros) on the internal hard drive on the Fast SCSI-2 
>bus and backed it up to the VXA drive and then to the DDS-2 drive 
>using Retrospect 4.2. Here are my results (avg):
>VXA: 44 MB/m (46 copy/42 compare)
>DDS-2: 94 MB/m (60 copy/214 compare)
>Overall the DDS-2 drive is over twice as fast as the VXA, a tad 
>slower on copy, but 6 times slower on compare!.

In Retrospect the settings are set up to allow hardware compression. 
The VXA drive is installed in the middle of the three scsi devices on 
the internal bus (CDROM-1, VXA-2, Hard Drive-3 (hard drive 
terminated). Hard Drive SCSI ID=0, VXA=2, CD-ROM =3. No other jumpers 
are enabled on the VXA drive.

In day to day use backing up network clients the speed difference is 
not as big. The VXA averages in the 40-50 MB/m range while the DDS-2 
drive averages in the 50-70 MB/m range.

I wrote to Ecrix and they stated this was a known problem with 
Retrospect and that I should contact them. So I did and they stated 
that this was not a known problem but that the max SCSI throughput 
one would expect on a Mac is around 95 MB/min (which matches what I 
have seen with the DDS-2 drive).

Everything in the setup favors faster speeds for the VXA drive yet it 
consistently delivers at least 25% slower speeds. So I'm not sure now 
if there really is some weird Retro slowdown conflict with the drive 
or if there is some just funky hardware problem with this particular 
drive, or the SCSI ribbon, or?? The max speed I can obtain doing a 
Finder copy from the internal Fast SCSI-2 drive to a drive on the 
slower external bus is around 3 MB/min... so this would seem to be 
the top bottleneck speed... well above what the VXA is giving me, so 
it doesn't seem to be the SCSI bus.

Has anyone else been using a similar configuration without any speed 
issues? If so, what is your exact setup like?

Thanks in advance,
-Greg Morin

Gregory Morin, Ph.D.  ~~~~~~~IS Manager~~~~~~~~~~~~~~~~~~~
Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM

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