Re: HP StorageWorks DAT 72 USB and Tape capacity (2137 Views)
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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 1 of 10 (5,734 Views)

HP StorageWorks DAT 72 USB and Tape capacity

[ Edited ]

Hello, I am bought older HP StorageWorks DAT 72 USB (DW027A) for my personal backups. I am using original tapes HP DAT 72 (C8010A) for data a HP DDS (C5709A) for head cleaning as well.

 

As I understand there should be possible to store 36 GB (or more precise 33,5 GiB) of compressed data on tape C8010A.

 

Unfortunately this is absolutly unachievable capacity for me. Capacity which I am able to store vary each time, even if I am trying to store the same data on the same tape (after tape full erase), and it is always less than 25 GiB :mansad:

 

I am doing backups in Linux this way: tar cvf /dev/st0 data-to-store

and data are several files (mostly less than 50) with capacity from several megabytes to several gigabytes - everything is compressed by BZIP2 with commpression level set to 9 (which is max).

 

I am tried to create one big TAR file from all data prepared for backup to see if there is some overhead which can steal valuable gigabytes from tape, but I am found that capacity difference between big TAR and untared data is absolutely meaningless.

 

So, is there anything what I am doing wrong, or can I do something to be able store more data on the tape (at least 30 GiB), for example switch-off automatic tape compression if is it used?

 

I will be glad for any help. Thanks.

 

 

P.S. This thread has been moved from Tape Backup (Small and Medium Business) to Tape Libraries and Drives.
-HP Forum Moderator

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Acclaimed Contributor
Dennis Handly
Posts: 24,746
Registered: ‎03-06-2006
Message 2 of 10 (5,711 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

[ Edited ]

The DAT 72 will only store 72 GB if it can compress 2:1, so you understand that.

Especially since your data is already compressed.

 

If your tape is marginal or you don't provide the data to the drive fast enough, you may lose space to this retries.

 

>for example switch-off automatic tape compression if is it used?

 

You may need to use this, if compression of already compressed data, it may make it bigger?

 

 

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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 3 of 10 (5,670 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

Hello Dennis,
Thank you and sorry for last response, I am lost this topic due to its moving by admin.

It is very interesting idea regarding this data copying speed. I will try connect DAT drive to a more powerfull computer with faster USB ports and I will see what happen.

Regarding data compression switch-off, any idea how to do it? I can't find way to do it.
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Acclaimed Contributor
Dennis Handly
Posts: 24,746
Registered: ‎03-06-2006
Message 4 of 10 (5,662 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

[ Edited ]

>I am lost this topic due to its moving by admin.

 

You can always see your posts by clicking on your name:

http://h30499.www3.hp.com/t5/user/viewprofilepage/user-id/1456815

 

>data compression switch-off, any idea how to do it?

 

You might want to ask this in the Linux board:

http://h30499.www3.hp.com/t5/System-Administration/bd-p/itrc-188

 

And provide a link to this topic, if helpful.

 

 

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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 5 of 10 (5,567 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

I am tested copying data to my DAT 72 on really fast computer with fast USB ports, so there shouldn't be any problem with speed with which data are going to the DAT. Unfortunately without success, I am still able copy to 36 GB tape only about 24 GiB of date compressed by BZIP2 :-/

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Occasional Advisor
Jim_Walls
Posts: 6
Registered: ‎05-24-2011
Message 6 of 10 (2,386 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

You are probably not achieving data streaming to the tape. Data streaming requires long blocks to maintain constant movement of the tape. Tar does not produce large enough blocks. Pipe the data through dd to obtain more optimum block lengths: tar -cvf - data-to-store | dd bs=64k of=/dev/st0

Adjust bs to achieve maximum throughput.
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Acclaimed Contributor
Dennis Handly
Posts: 24,746
Registered: ‎03-06-2006
Message 7 of 10 (2,374 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

>tar does not produce large enough blocks.

 

tar(1) does have a -b option to set the blocksize.  Not sure if that can be as large as dd(1).

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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 8 of 10 (2,369 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

Thank you for the tip. I will test it on the evening, when I will return at home.
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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 9 of 10 (2,137 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

So, I am tried both options - tar with -b parameter, and method via dd, but unfortunately I must say, than results are still the same - I am able store only 21 GiB of my testing data to the tape, which is 10 GiB less than declared tape capacity :-/

 

I will try to find some original Windows backup software from HP, and I will try to do testing backup if results will be different.

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Occasional Advisor
corwin78
Posts: 7
Registered: ‎10-17-2013
Message 10 of 10 (128 Views)

Re: HP StorageWorks DAT 72 USB and Tape capacity

At least I have had opportunity to test TAPE drive under Windows. I am downloaded some Iperius application, and with it I was able store 28,6 GiB of data to TAPE (the same data and the same tape like under Linux).

 

So, obviously drive is working correctly, and it must be some configuration issue under Linux to be able store more data.

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