> 
> So here's an interesting issue I thought I'd run by the mailing list.
> 
> Master Server = Sun E250 (NBU 3.4_3)
> Media Server = GS80 running Tru64 (NBU 3.4_3)
> STK L80 with (8) DLT8000 direct SCSI attach (3 meter cables)
> 
> The media server is backing up raw devices to tape but I'm getting strange
> performance numbers.  When I backup a brand new raw device without any data
> on it (i.e., just added to the system) my throughput is great, around
> 12.5MB/sec to tape.  But once I actually use this device (pull it into a
> disk group and plop a filesystem on it with data) my throughput for backing
> up this raw device drops to around 5.5MB/sec to tape.  This is happening for
> all the disks.
> 
> Maybe I'm missing something here but I thought a raw device was a raw device
> regardless of the data on it?  Anyone seen this kind of behavior before?
> Thanks.

Speculation, but I'd imagine that your raw devices immediately after
initialization are probably filled with zeros.  Also, you may be running
your tapes with hardware compression.  If so, your performance may be
related to the compression the drive is able to get.

While I would expect higher rates on a 8K drive, it may be you have
other points that are slowing down, but that the drive is part of it.

You should be able to tell if the device itself is involved with some
'dd' testing...  'time dd if=/raw/device of=/dev/null bs=64k'

I'm also assuming that you're *not* doing client side compression on the
raw device.  If so, that might affect it even more...

-- 
Darren Dunham                                           ddunham AT taos DOT com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >