From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] poor mysqldump performance
Date: Sat, 25 Feb 2012 03:13:27 +0100 [thread overview]
Message-ID: <20120225021327.GA23278@tansi.org> (raw)
In-Reply-To: <20120224223020.GV22456@tracyreed.org>
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@wagner.name
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
next prev parent reply other threads:[~2012-02-25 2:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-23 22:23 [dm-crypt] poor mysqldump performance Tracy Reed
2012-02-23 23:10 ` Arno Wagner
2012-02-23 23:59 ` Tracy Reed
2012-02-24 8:18 ` Milan Broz
2012-02-24 19:07 ` Tracy Reed
2012-02-24 20:05 ` Arno Wagner
2012-02-24 22:30 ` Tracy Reed
2012-02-25 2:13 ` Arno Wagner [this message]
2012-02-24 1:29 ` Alasdair G Kergon
2012-02-24 2:55 ` Tracy Reed
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