Re: [Bacula-users] tape marked full, but has 340GB free, now says 635 billion bytes for a 400GB tape.

[Nick J. <nic...@ui...>]

I apologize, I understand compression and read the FAQ and documentation.

My question arises amidst earlier tape errors with this particular
tape and the fact that all the other tapes become full at just over
400 billion bytes, or 400 gigs.

So, ok, all of a sudden compression is on.  I think it must have been
enabled when I was messing with btape trying to test the "bad" tape.
If this is the case though, then I wonder why compression wasn't
enabled the first time I ran btape on these exact same tapes/drive
(note: on the last run of btape I terminated (killall) the btape
console after it froze on me, which may explain that).

I'm just going to wipe the pool and jobs and start over, after running
a btape fill on this tape.

Thanks for pointing that out.

Nick

ps.
[root@lcn ~]# tapeinfo -f /dev/sg2
Product Type: Tape Drive
Vendor ID: 'HP      '
Product ID: 'Ultrium 3-SCSI  '
Revision: 'G24H'
Attached Changer: No
SerialNumber: 'HU10534WE1'
MinBlock:1
MaxBlock:16777215
SCSI ID: 4
SCSI LUN: 0
Ready: yes
BufferedMode: yes
Medium Type: Not Loaded
Density Code: 0x44
BlockSize: 0
DataCompEnabled: yes
DataCompCapable: yes
DataDeCompEnabled: yes
CompType: 0x1
DeCompType: 0x1
Block Position: 22658
[root@lcn ~]#

On 1/25/07, John Drescher <dre...@gm...> wrote:
> On 1/25/07, Nick Jones <nic...@ui...> wrote:
> > I had a bad tape recently
> >
> > I have tried to verify if the tape is good or not, but I've run into
> > another issue.
> >
> > It now wrote the tape fine, and didn't error out at
> > Bytes=52,398,230,131.   However, it wrote way more bytes that what
> > will fit on the tape.  It is a 400 GB LTO-3 tape.
> >
> > |      22 | tape7      | Full      | 635,479,838,715 |      636 |
> > 15,552,000 |       1 |    7 |         1 | LTO       | 2007-01-25
> > 08:52:41
> >
> > Can anyone explain how the drive wrote so much data, or why it *thinks* it did.
> >
> The drive has hardware data compression that saves tape space by
> compressing each packet sent to the drive. Although the manufacture
> will claim 2:1 (and call the tape a 800GB tape) is the norm this
> number is highly dependent on your data. Remember that compressed data
> does compress a second time and random data is also not compressible
> but text is very compressible.
>
>
>
> BTW (dev team), Is this info in the docs or faq anywhere? I believe I
> have answered this question 20 times or more ....
>
> John
>


-- 
Nick Jones
University of Iowa
Dept of Neurology
Systems Analyst
319-356-0451