Hi,
I´ve got the same kind of problem, not only with DDS-[234] tapes, but
also with "all-powerful-with-bells-and-whistles" AIT-3 units, with
controllers ranging from Adaptec stock 2940 to PCI-X Ultra-320... almost
same results.
The problems seems to lie in tar itself; I read there´s something to
do with block sizes, but using -b with larger values got me not much
more than corrupt or incomplete data. :( The only way I got to have
decent transfer rates AND reliability was to filter *archiving* through
dd, including block sizes. For example, to archive:
# tar -zcpf - /usr/local | dd of=/dev/sa0 bs=64k
and to restore:
# tar -b 128 -zxvf /dev/sa0
The above is particullarly true for remote transfers; if you´re using
tar over rsh/rmt (-f host:/path), you´ll surely prefer simple "rsh/tar"
with output redirection. ;)
Note that block sizes in tar count as 512-byte ones, while in dd they
can be specified as Kilobytes or even megabytes. Besides speed, there´s
a sensible boost on storage space when using dd-block-sized transfers.
The apparent reason for that is tar actually uses -b 20 (10kb) blocks,
while 10GB+ tapes usually expect larger sizes.
For AIT-3, I didn´t notice any real good improvement past 128kb block
sizes; I didn´t experiment enough with DDS-4 because our test tape drive
got a heart attack and quit... BTW, it returned 2 weeks ago and I didn´t
give it any attention; it may be a little depressed by now, so I guess
I´ll return it to test beds. :) Anyway, I wouldn´t try anything lower
than 32kb blocks on it.
I can´t remember if I did any test pointing to /dev/null, as mr.
Hartland suggested, nor from /dev/zero or /dev/random... it´s worth a try.
I´ll post new results as soon as I get´em (if any). ;)
Have luck,
Tulio G. da Silva
Steven Hartland wrote:
Might be silly but do u get similar results if u:
1. expand to a memory backed disk
2. expand to /dev/null
Steve
----- Original Message ----- From: "JG" <[EMAIL PROTECTED]>
I had to unpack a lot of tar archives and I occasional noticed terrible
bad performance on freebsd5.
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