Restore from Raw device taking longer time

[Richard Lopes]

Hello,
I have taken backup of my database residing on raw partitions to regular files on filesystem.Although the backup operation is completing fast, when I do the restore after recreating the raw logical volumes, it is found to be taking too long time to finish. In my case 5GB is taking less than 10 minutes to backup. But takes 1 hour for restoration.I tried with block sizes of 2048 and 8192.Same effect. I have tried to directly take the backup on a LTO Ultrium tape drive.Same problem while restoring.

Is there any issue with regular file to raw file conversion?

But my restore has worked fine and database is getting restored properly. The only issue is the longer time taken in restore.

Any valuable suggestions?

Thanks and Best Regards,
Abdul Salam

[Hein van den Heuvel · Accepted solution]

The block sizes you tried are unreasonable small. Do the math: 5GB / 2048 = 2621440.
3600 second/hour.

If you restored in 1 hour you did 2621440 / 3600 = 700+ IO/sec. That is likely to be the max for unbuffered single stream, non-async
IO. The system can surely handle many more MB/sec, but single stream waiting for each Io to be finished before starting the next can not drive more IO/sec.

Try a block size of 1MB, or at the very least 128KB: bs=1024k?

When you where taking the backup the file system some component(s) enabled read-ahead making it more efficient.

Also... are you compressing the DB raw device during the backup? You probably should. It tends to be well worth it.


Hth,
Hein.

[Richard Lopes]

Hi,

Many thanks for the response! I had setup a block size of 8192k for "dd" and got 5GB data restored in around 6 minutes (regular file to raw device)

I'm going to try it directly from tape to raw device and see how long it takes.

Thanks and Best Regards,
Abdul Salam