"mt status" output

[Claudiu Ionescu]

Hi,

Could you help me please with the following:

I've just attached a SDLT320 device at my HP-UX server in order to do a full backup.
Running "mt status", I got:

# mt status
Drive: QUANTUM SDLT320
Format:
Status: [41119386] BOT online compression immediate-report-mode
File: 0
Block: 0
#

What does it mean "[41119386] BOT online compression ", in fact "41119386"?
I know that BOT = Begin of Tape, but I wish to backup some data at about 42GB, and I put inside a 160GB/320GB(compressed) tape.
Is it possible to backup the entire data, or only a part?

Thank you in advance,
Claudiu

[Calandrello]

Friend
in command TM /dev/rmt/xxmn he shows the status of the unit if the type of writing will be compressed way software can use the total capidade for writing of the ribbon.

[Claudiu Ionescu]

Calandrello,

I was using the "/dev/rmt/0m" option, that means it's about BEST density (Highest-capacity density or format will be used, including data compression, if the device supports compression.), but I'd like to be sure that I'll be able to write 42GB on the tape.
That's way I am a little bit confused due to the fact that the response says something about [41119386].
What does it mean, that only 41119386 bytes could be backup?
Or this is regarding to the position of the writting header?

Thank you in advance,
Claudiu

[Kent Ostby]

I believe that this is a known issue with HP's mt command that it does not return the format string for a tape with that high of density.

If this is a big issue for your business, you may need to contact HP for a fix.

[Claudiu Ionescu]

Dear Kent,

Thank you too for your answer.
In fact I am not interested in the fact that the format string is not correctly returned for a tape with that high of density.
What I really wish to know is what represent the nnnnnnnn integer from the output of the "mt status":
# mt status
Drive: QUANTUM SDLT320
Format:
Status: [nnnnnnnn] BOT online compression immediate-report-mode
File: 0
Block: 0
#

So, I wish to be sure that the tape that has just been inserted (160/320GB) is able to backup more than 41119386.
41119386 means 41GB?

Also, I am a little bit confused due to the fact that the "man mt" contains for "status" switch only: "Print status information about the tape drive", but there is no information regarding to what the nnnnnnnn integer number really represents.

Thank you in advance,
Claudiu

[Coolmar]

Hi Claudiu,

Is your device working properly? Can you do a quick tar or dd to the tape? I found the following link....I don't think it gives you the info that you ask for, but it is the same error and might get you in the right direction.

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=1073180&admit=-682735245+1165239554626+28353475

[Pete Randall · Accepted solution]

Claudiu,

I'm guessing that the 41119386 is the system's response to the mt system call - it is the numerical answer returned.

For example, I have a DLT8000 drive with a capacity of 40GB:

Drive: QUANTUM DLT8000
Format:
Status: [41118985] BOT online compression immediate-report-mode

And I also have a SDLT320 with a capacity of 320GB:

Drive: COMPAQ SDLT320
Format:
Status: [41119386] BOT online compression immediate-report-mode
File: 0

Obviously the 4111nnnn response can not have anything to do with the capacity of the tape.


Pete

[Bill Hassell]

Unfortunately,k tape drives do not have a common standard to report the native capacity, so the mt status command does not provide any capacity data. You must know the model of the tape drive *and* the tape you are using. Many tape drives will record at different capacities depending on the tape you use. But you cannot use a tape that is not compatible with the drive.

Note that the SDLT 320 tape drive records 160Gb of data -- no more!!! It has been a common industry practice to overrate tape drives by 100% because the compression circuitry can reduce the amount of data sent to the tape, and with certain data patterns, this compression can reach 2:1. But you cannot easily predict how much reduction a particular collection of data will have. You will always get the native capacity -- anything more is nice, but not guaranteed.

It is a common mistake to use a simple backup program (like tar or cpio) and use the 2:1 compression ratio to pick a tape drive so everything fits. Eventually the data won't fit and the simple tool falls apart because it knows nothing about loading another tape. This is especially true for databases as they expand during the year and become less compressible.

Also be aware that today's high performance tape drives require enormous amounts of data to keep them streaming. If the system (CPU+disk+backup program) cannot reach this speed, the tape will have to resync and this can increase the backup time 300% to 1000% as well as massively increasing wear on the drive.

[Claudiu Ionescu]

Dear All,

1./ Regarding to the Coolmar's message, I've checked that the tape is working fine using the fbackup and frestore commands; also, I got the index of the tape and it was ok.
Therefore, I consider that the tape is working ok.

2./ Regarding to Pete Randall's massage, I've just typed the "mt status" command on another HP-UX machine having a DDS3 tape device, and the response was the following:
# mt status
Drive: HP C1537A
Format: DDS-2 format
Status: [45112400] BOT write-protected online compression immediate-report-mode
File: 0
Block: 0

So, taking into consideration that a DDS3 could write only 12GB, for sure that the 45112400 number does not represents the available capacity.
So, Pete has definitely right.

3./ Regarding to Bill Hassell's message, I'll take into consideration all your advices, and I'll be very carrefully from now on at the amount of data to be backup.

Thanks a lot to everybody.

Best Regards,
Claudiu

[Bill Hassell]

Just a few notes about fbackup:

- fbackup is definitely the best choice and will keep the tape drive busy, assuming that the drive has it's own dedicated I/O card in the computer

- fbackup does handle multiple tapes just fine. It will pause when the first tape is full and request the next tape.

- to maximize the speed at which fbackup runs, be sure to include the -c option in your backup script. Your -c config file should look like this:

blocksperrecord 4096
records 64
checkpointfreq 4096
readerprocesses 6
maxretries 5
retrylimit 5000000
maxvoluses 200
filesperfsm 2000

[Dennis Handly]

The status field is a hex number from ioctl(fd, MTIOCGET). Some of the bits are decoded into those words after the hex number in []. BOT is the "4" and the two nibbles 93, is the density. This shows up in as: #define DEN_DLT_190000_56c 0x00000093 /* 56 trk, compressed, 320.0GB (2:1)*/

Ordinarily the density code should occur just before the "BOT". As Kent said, you probably should contact the Response Center to get your model supported by mt(1). An obvious search doesn't indicate any enhancements filed on this. I filed CR JAGag25648 to get this fixed.

[Claudiu Ionescu]

Dear Dennis,

Thank you for your answer that's very useful for me.

Best Regards,
Claudiu

[Claudiu Ionescu]

Thanks to the answers received from the Forum's members, I consider that I could close this thread.
Thanks to everybody.

Best Regards,
Claudiu