DLT7000 block size

[Gabor Melis <mega@hotpop.com>]

This box is a Dell Poweredge 2600 running Debian/Sarge with kernel 2.6.8. The 
problem is with the tape:

# tar cf /dev/st0 /lib/modules/2.6.8-1-686-smp/
# tar xfv /dev/st0
<produces nothing or "Cannot allocate memory">

After heavy googling I tried passing tar the block size explicitly with -b 
(for both invocations). It is not until '-b 216' that tar finally manages to 
read back the archive. I can find no documentation for the Quantum DLT7000 
that mentions a minimum block size and since it is a critical server I'm a 
bit worried about this magic number that _seems_ to make it work.

I tested it with the default stinit.def and the one below.

Gabor Melis

# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: MegaRAID Model: LD0 RAID5 39760R Rev: 2.48
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 04 Id: 06 Lun: 00
  Vendor: PE/PV    Model: 1x6 SCSI BP      Rev: 1.1
  Type:   Processor                        ANSI SCSI revision: 02
Host: scsi0 Channel: 05 Id: 06 Lun: 00
  Vendor: QUANTUM  Model: DLT7000          Rev: 2561
  Type:   Sequential-Access                ANSI SCSI revision: 02

# mt -f /dev/st0 status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x85 (DLT 35GB compressed).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN

# cat /etc/stinit.def
{buffer-writes read-ahead async-writes}

manufacturer="QUANTUM" model = "DLT7000" {
scsi2logical=1
can-bsr
auto-lock=0
two-fms=0
drive-buffering=1
buffer-writes
read-ahead=1
async-writes=1
can-partitions=0
fast-mteom=1
#
# If your stinit supports the timeouts:
timeout=3600 # 1 hour
long-timeout=14400 # 4 hours
#
# Drive is backwards compatible, use older modes (e.g. from above) as 
required.
mode1 blocksize=0 density=0x85  # 35GB + compression
mode2 blocksize=0 density=0x84  # 35GB, no compression
mode3 blocksize=0 density=0x83  # 20GB + compression (DLT4000 mode)
mode4 blocksize=0 density=0x82  # 20GB, no compression (DLT4000 mode)
}