[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: poor mysqldump performance



On Fri, Feb 24, 2012 at 02:30:20PM -0800, Tracy Reed wrote:
> On Fri, Feb 24, 2012 at 09:05:29PM +0100, Arno Wagner spake thusly:
> > Blocks used in dm-crypt are allways 512 Bytes in size, hence no extra reads
> > or writes compared to non-encrypted disks should ever be required. 
> 
> Ok, so there goes that theory.
> 
> > Please to not. ECB is massively insecure. And it will not result in reading
> > less data. Well, you can do it as an experiement, but please do not use it
> > when it has to be secure.
> 
> I already did a test with it and as you correctly expected, it made no
> difference. We certainly won't be deploying ECB. I am aware of the same
> plaintext security issues with it.
> 
> > It should not. But if you notice a difference, it may be interesting to see
> > what it is.
> 
> I found no difference.

As expected. Still good to know, sometomes these assumptions turn
out to be wrong.
 
> > There is also another possible factor that may make a larger or smaller
> > difference: If I remember correctly, you said the dump was going to the same
> > disk, but from different partitions for encrypted and non-encrypted. This may
> > influence speeds. First, head seeks are dependend on seek distance. The
> 
> You remember incorrectly: The dump is being done using mysqldump on a remote
> machine. So it is going over the network and writing to totally different
> disks.

Ah, sorry.

> > regions have different data density. My observation is that disk linear
> > throughput drops to less than half towards the end of many disks.  And third,
> > you may have a different fragmentation or data placement situation or
> > filesystem parameter on both source disks.
> 
> This is a very good observation and could be part of the problem here. I have
> been using different logical volumes on the same disk. I will try using the
> same LV mapped with dm-crypt vs no crypto and see if that helps.

It would be an easy explanation. Let us know about the results.

> Thanks!

No problem.

Arno
-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@xxxxxxxxxxx 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
----
One of the painful things about our time is that those who feel certainty 
are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell 
_______________________________________________
dm-crypt mailing list
dm-crypt@xxxxxxxx
http://www.saout.de/mailman/listinfo/dm-crypt


[DM Devel]     [Fedora Desktop]     [ATA RAID]     [Fedora Marketing]     [Fedora Packaging]     [Fedora SELinux]     [Yosemite News]     [Yosemite Photos]     [KDE Users]     [Fedora Tools]     [Fedora Docs]

Add to Google Powered by Linux