Jon Lewis wrote:
> On Fri, 4 Dec 1998, Pete Popov wrote:
>
> > The lower than expected performance is most likely due a small SCSI transfer
> > size. I increased the default 32K to 128K, recompiled the st driver, and use 128K
> > with tar and regularly get 70MB/s with my SDT-7000.
>
> Since I got around half the advertised speed, I just started wondering if
> maybe I'd accidentally done the backups with compression off...but I
> double checked, and my script did have mt set compression on.
> > The 1.5MB/s (90MB/min) spec is the actual transfer rate to tape.
Oops, it's been a while since I worked on the 7000. The transfer rate to tape
is 777KBps, not 1.5MB/s. The 1.5 assume 2/1 compression.
> You'll need an extremely fast host with low SCSI command overhead to get close
> > to that.
>
> The system used as the tape host is a lowly P100, but does have a nice new
> Diamond Fireport 40. Maybe it just can't keep up.
The only systems that came somewhat close to the max transfer rate were the DEC
Alphas we had. Otherwise you really can't expect the system to have a low
enough SCSI command overhead to be able to keep the drive streaming at
its max rate all the time. However, as I mentioned, I do get around 70MB/s
with my drive when the total scsi transfer size per write command is 128KB.
Pete
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