Can't get C1553A to Compress...

[Lenny Story]

Greetings,

I have a surestore 12000e Autoloader (C1553A), and i cannot seem to get the compression to work.

I am writing a 1GB file which contains the repeated string :

This is a test of the emergency Broadcast system. 0123456789ABC
This is a test of the emergency Broadcast system. 0123456789ABC

I have enabled the compression using the command : mt -f /dev/nst0 datcompression 9.
The DC indication on the drives front panel is on. It is my guess that a file containing the same repeated value should compress to almost nothing.

The dip switches on the bottom of the drive are all on Except for 3 which is off.

My tests have consisted of rewinding the tape, and executing the command "tar -cvf /dev/nst0 gigfile.txt" with and without datcompression on. In both cases the "mt tell" command reports the same block location when finished. (104858).

Does anyone have a clue what im doing wrong ?

Thanks,
Lenny
---------------------------------------------------

root@skunk:/home/catbert > cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 02 Lun: 00
Vendor: HP Model: C1553A Rev: 9608
Type: Sequential-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 01
Vendor: HP Model: C1553A Rev: 9608
Type: Medium Changer ANSI SCSI revision: 02
root@skunk:/home/catbert >

---------------------------------------------------

root@skunk:/home/catbert > mt -f /dev/nst0 status
drive type = Generic SCSI-2 tape
drive status = 603990016
sense key error = 0
residue count = 0
file number = 1
block number = 0
Tape block size 10240 bytes. Density code 0x24 (DDS-2).
Soft error count since last status=0
General status bits on (81010000):
EOF ONLINE IM_REP_EN
root@skunk:/home/catbert >

---------------------------------------------------
root@skunk:/home/catbert > mtx -f /dev/nst0 inquiry
Vendor ID: 'HP ', Product ID: 'C1553A ', Revision: '9608'

---------------------------------------------------

root@skunk:/home/catbert > mtx -f /dev/nst0 status
Data Transfer Element: Full (Storage Element 1 Loaded)
Storage Element 1: Empty
Storage Element 2: Full
Storage Element 3: Full
Storage Element 4: Full
Storage Element 5: Full
Storage Element 6: Full
root@skunk:/home/catbert >

---------------------------------------------------

root@skunk:/home/catbert > cmtape


Device : /dev/nst0
Type : Generic SCSI-2 tape
---------------------------------------
Current File : 1
Current Block : 104858

Errors :
---------------------------------------
Sense Error : 0
Residue Count : 0
Software Errors : 0

Status : 24002800
---------------------------------------
Block Size : 10240 (0x2800)
Density : 36 (0x24)


General Status : 0x81010000
---------------------------------------
* End Of File
* Online
* Immediate Report Mode

[BR19682]

Hi there.
Pls do not be bothered, but tar is already compressing the data.
Try a dd to tape with a file or directory
with compression on and off.
For the parameters of dd pls check the manpages.
Rgds
Alexander M. Ermes

[Lenny Story]

Greetings,

Actually, tar is not compressing the data as I did not include the -z option.

Tar's only operation in this case is to create a single file which contains all of the backup data. Nothing more.

-Lenny

[CA633962]

Hello Lenny,
you might check this without host control, the drive has the possibility to switch compression on and off, also you can switch off the control from the host. With this you can be sure if Hardware compression is working and you are able to say if the hardware or the configuration is the problem.
there are 8 switches on the drive, normally all set to 8 and only switch 3 is set to off.
Switches 1 and 2 are responsible for it. Here the description:
Switch 1 Switch 2 Meaning
On On Compression enabled at power-on with host control
On Off Compression enabled at power-on no host control
Off On Compression disabled at power-on. The host is allowed to control compression.
Off Off Compression disabled at power-on no host control


I would test with both off and sw 1 on/ sw 2 off, then compare the results.

That should show that compression is working. Than you need to check device files or driver configuration.

I hope this helps to troubleshoot this.

Best Regards,
Ralf