Date: Fri, 03 Jul 1998 01:27:35 -0400 From: Harlan Stenn <Harlan.Stenn@pfcs.com> To: dc-sage@dc-sage.org, scsi@FreeBSD.ORG, amanda-users@cs.umd.edu Subject: DDS/2 tape specs Message-ID: <596.899443655@brown.pfcs.com>
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I wanted to see how much data could be written to a DDS-2 120M 4mm tape. I have an ARCHIVE Python 28388-XXX 4.98 drive on ID5, and: bt0 <Buslogic 946 SCSI host adapter> rev 0 int a irq 11 on pci0:11:0 bt0: Bt946C/ 0-(32bit) bus bt0: reading board settings, busmastering, int=11 bt0: version 4.25J, fast sync, parity, 32 mbxs, 32 ccbs ... bt0: targ 5 sync rate= 5.00MB/s(200ns), offset=15 I wrote 8k blocks. My first test did a "dd" copy of /dev/urandom to the drive: % dd bs=8k if=/dev/urandom of=/dev/rst0 dd: /dev/rst0: Input/output error 413953+0 records in 413952+0 records out 3391094784 bytes transferred in 18181.953012 secs (186509 bytes/sec) My second test took 8191 `y' characters followed by a newline: % yes `cat 8ky` | dd bs=8k of=/dev/rst0 and I eventually killed after over 24 hours' elapsed time. When I killed it, I think it claimed to have written nearly 10G to the tape. My third test copied 2 4G (reasonably full) filesystems to the drive: % cat /dev/sd1c /dev/sd2c | dd bs=8k of=/dev/rst0 dd: /dev/rst0: Input/output error 797354+0 records in 797353+0 records out 6531915776 bytes transferred in 15816.188468 secs (412989 bytes/sec) Just for grins... % tcopy file 0: block size 8192: tcopy: read error, file 0, record 797349: Input/output error I then rewound the tape, did a "mt fsr 787349" followed by "mt weof 100000", but the "weof" part finished Immediately and without error, so I didn't believe it. For my last test, I did: % while ( dd bs=$size if=/dev/sd1c of=$mt count=3 && mt weof 3 ) ... 3+0 records in 3+0 records out 24576 bytes transferred in 0.053951 secs (455525 bytes/sec) mt: /dev/nrst0: weof: Input/output error Did 249699 reps... (the "while" loop had a counter in it) so 249699*3=749097 8k blocks... Assuming the same density for the previous case, which did 797353 8k blocks... or .93947975 is data, which means that .06052024 is "tape mark space". This means that: .06052024 * 6531915776 bytes / 797353 tape marks or 528 bytes/tape mark is "tape mark space". Summarizing: The tape drive can write at about 400k/sec A 120M 4mm tape can hold about 3.3G of random (compressed) data, or 6.3G of normal filesystem stuff A tape mark uses about 600 bytes of space. Am I missing anything? H To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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