Backup speed fluctuation.

[pmidds]

Hi,

whilst backing up we're getting anything from speeds of 21 MB /s to 180 Kb / s.

Anyone know why there's such a descrepency and how we could make it stay up the high end of through put speed a bit longer ? I've played around with parrelelism but this doesn't seem to have had much effect.

Thanks in advance.

 

[sdeb]

The reason must be the kind of files you are backing up. You'll have that problem with most of the tape devices.

Keep in mind that you'll have nice throughtputs with big an not compressed files, and (very) poor throughtputs with small compressed files.

This is due (to explain it easily) to the fact that the tape drive must use its buffers before writing to the tape and it takes longer to handle small files that bigger ones, and in that case the drive fill buffers /write /stop /fill /wrties / stop Etc... with bigger files the drive nearly never stop (and positioning takes also a long time).

You can try to backup other devices or servers at the same time or maybe to first stage data to a disk device...

 

[605]

I agree - if you can achieve maximum speed, which you can easily
test using "bigasm" (see the Performance Tuning Guide, PERFTUNE.PDF
for details), it must be the file size. Just create a directory
of files all of a certain size and then back it up. Files with
a size up to 100kB will cause such problems, if they represent
the majority of the files involved. There is an interesting
article available on Legato's PartnerNet page:
- Search for "13/2003"
- Download the "Technical Info Document 13/2003"