Speed on using TAR

[Patrick Chim]

Hi,

I am using TAR to backup all the oracle datafiles onto a DLT8000 tape drive. They only have 3.5GB data but I found that it takes more than half hour to tar the files. Is it reasonable ? Is there a quicker method to backup the files using tar ? Also I cannot find any option of tar to specific the block size. Is that true ?

Regards,
Patrick

[Elmar P. Kolkman]

I had the same problem. I would suggest you look for ftio. That's a lot faster. You could also try to set larger blocksize and set the DLT for no compression.

[Steven E. Protter]

You need to know the top speed of the tape drive and the scsi card the drive is hung from to evaluate whether you are getting appropriate speeds.

You can try fbackup.

Either fbackup or tar will not get good copies of the data unless the database is down for backup.

Other factors influencing speed include other devices in the scsi chain with the tape drive. This is bad for it degrades speed.

Another factor is how much activity on the disk device when you are running the backup. If this is a very busy system your speed is reasonable. If not, you need to provide more information to get a useful opinion from me.

SEP

[John Palmer]

Tar is OK but beware that in standard release form, it won't handle large files (> 2Gb).

You should be able to get 5-8Mb/sec to your DLT (roughly 2-3 minutes per Gb) provided you increase the blocksize that it writes to tape.

Use -b 64 to set the blocksize to 64Kb.

I've never found any situation where it's been necessary to disable hardware compression on the tape drive. In my experience, Oracle datafiles tend to compress fairly well.

Regards,
John

[Jean-Louis Phelix]

Hi,

I'm not sure that using a simple tar to backup on a DLT is good. DLT can write much faster than tar can read and I'm not sure that you can reach the required speed for "streaming mode". In this case your DLT will always start and stop. This could even damage you DLT. Diabling compression could be an improvment, but using a real backup tool with many readers would be the best.

Regards.

[Elmar P. Kolkman]

Exactly. That is the moment turning off compression helps... Then the speed you have to write with to keep the tapedrive streaming (and thus fast) is the same no matter what kind of data you are trying to write.

If that is slow too, try doing a dd to the tapedrive from something like /dev/zero and /dev/random if you have them, to test the DLT drive. I had a faulty tapedrive (DLT8000 too) a year back and was looking at the software for the cause, when after 2 weeks of testing we were able to proof by using another tapedrive that the tapedrive was faulty... We could only get it streaming with /dev/zero, but as soon as the data was not all zero's, the speed dropped to a crawl.

[Michael Schulte zur Sur]

Hi Patrick,

this makes it less than 2mb per second, which is slow. Which device are you using?

Hi SEP

you cant say that backup isnt good, when the database is open. Set tablespaces with begin backup and it works also.

greetings,

Michael

[Geoff Wild]

Fbackup is faster then tar - but I'd put the db in "hot backup mode" when doing a backup....

"fbackup combines features of dump and ftio to provide a flexible, high-speed file system backup mechanism (see dump(1M) and ftio (1))."

Some other posts:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=14799

A tble comparison of backup utilities:

http://docs.hp.com/cgi-bin/fsearch/framedisplay?top=/hpux/onlinedocs/5187-2216/5187-2216_top.html&con=/hpux/onlinedocs/5187-2216/00/00/56-con.html&toc=/hpux/onlinedocs/5187-2216/00/00/56-toc.html&searchterms=fbackup&queryid=20031126-033157


Rgds...Geoff

[Michael Schulte zur Sur]

Hi Patrick,

are you still with us?

greetings,

Michael