topic Re: fbackup on dds3 tape in Operating System - HP-UX

fbackup on dds3 tape

Jerry P Antony_2 — Wed, 30 Mar 2005 08:22:28 GMT

Hi
Can I take more than 12GB data on DDS3 tape?Which device name should I use for that?
Regards
Jerry

Re: fbackup on dds3 tape

RAC_1 — Wed, 30 Mar 2005 08:29:05 GMT

Use lssf on all devive files and use which says best density.

Anil

Re: fbackup on dds3 tape

Patrick Wallek — Wed, 30 Mar 2005 09:06:57 GMT

That really depends on the data.

If the data is compressable, then yes. If the data is not compressable, then no.

Use /dev/rmt/0m

Re: fbackup on dds3 tape

Jerry P Antony_2 — Wed, 30 Mar 2005 09:15:48 GMT

My data is .tar files..I have total 19.5 gb data.I am using /dev/rmt/0m device name for taking fbackup.Backup started with dds3 tape.Then I put another 2* dds2 tapes, still asking for the next tape...

Re: fbackup on dds3 tape

Florian Heigl (new acc) — Wed, 30 Mar 2005 09:47:35 GMT

if it's simple tar files, could You consider compressing them before backup?

(/usr/contrib/bin/gzip is always available)

Re: fbackup on dds3 tape

Patrick Wallek — Wed, 30 Mar 2005 09:56:49 GMT

Again, it depends on how compressable the tar files are. The fact that the files you are backing up are tar files is irrelevent. The actualy contents of the tar files is relevent. Is it ASCII files? Database files? Pictures? Movies? Some other sort of data files?

Try compressing one of those tar files with gzip or compress. See if it gets any smaller. If it doesn't then the tape drive is *not* going to do any better and you should plan on multiple tapes.

You would be much better off keeping the tapes in the set the same. If you start backing up with DDS3, then stick with it. If you have 19.5GB of data that should easily fit on 2 DDS3 tapes at their native 12GB capacity.

Re: fbackup on dds3 tape

Hoang Chi Cong_1 — Thu, 31 Mar 2005 02:46:24 GMT

I am not sure that can backup with file size up to 12 GB.
Take a look with this thread:
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=753278

Regard
HoangChiCong

Re: fbackup on dds3 tape

Jerry P Antony_2 — Thu, 31 Mar 2005 02:51:51 GMT

Hi All
Thanks for the inputs.
jerry

Re: fbackup on dds3 tape

Bill Hassell — Thu, 31 Mar 2005 10:13:50 GMT

The only thing you are guarenteed on a DDS3 tape is 12Gb which is the uncompressed capacity of the tape. To turn on compression, you use a device file that has the text: "best density" in the lssf command:

lssf /dev/rmt/*

Using this device file will turn on the drive's compression which is about equal to any external compression utility. A tar file is not compressed, it is simply a concatenation of the orginal files with headers between each file, so there is nothing you can determine about the compressability of the data. You can run gzip or compress on one of your tar files to see what the difference is:

ll myfile.tar
compress myfile.tar
ll myfile.tar.Z

The difference is roughly how much compression will be used when you backup that file to tape. Average data compression on a basic HP-UX installation is just under 2:1 which means you can store just under 24Gb on the DDS3 tape. If you are backing up a commercial database that is only partially used, your compression ratio may be 10:1 or even 20:1 (in other words, you can store 120Gb on a DDS3 tape). But that is because the empty database typically contains long strings of nulls or is a sparse file. There really isn't 120Gb of data, just codes that indicate long strings of the same pattern.

Noted also that except for fbackup, when you restore a sparse file (where many records were never defined), all the missing holes in the restored file will be filled with nulls, thus occupying more space on the disk. This is normal and expected since if all the records are eventually used, the file would still be the same size. fbackup has an option (-s) which compresses long strings of nulls into directory entries that mark these blocks as undefined.

So all of this is to prepare you for the fact that the *only* amount of data that can be stored on any tape drive is the native capacity which is sometimes difficult to determine. The tape industry adopted the 'compressed model' more than a decade ago, calling a 12Gb DDS3 a DAT24, implying that it stores 24Gb. However, the fine print says: "assuming 2:1 compression". In Unix land, we say: "Your mileage may vary"

Here is a quick reference chart:

Tape type Length Native capacity
DDS1________60m____1.3Gb
DDS1________90m____2.0Gb
DDS2_______120m____4.0Gb
DDS3_______125m____12.0Gb
DDS4_______150m____20.0Gb
DDS72______180m____36.0Gb

More details:
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50457