[dm-crypt] Performance problems

[dm-crypt] Performance problems

[Joakim Reinert]

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Hello,

i intended to use dm-crypt + LUKS to encrypt my entire file system. I
ran into the following problem: After finishing cryptsetup i noticed
by testing with dd (dd if=/dev/zero of=/dev/mapper/cryptroot) with
different blocksizes, that i had read and write speeds of roughly
50MB/s. If you consider my setup, you will agree, that this is way too
slow:

cpu:        i7-2620 (AES-NI integrated)
disk:       Crucial m4 226GB SSD
ram:       4GB DDR-3 1333Mhz (Single Channel)

Additional information:

kernel:    linux 3.6.6.1
os:         arch linux

I have loaded the module aesni_intel and verified that the refcnt
changes in /proc/crypto when i open/close the encrypted partition.

I've already harrassed everybody at #archlinux and #crypto in IRC but
nobody seems to know what the problem might be. I also installed
truecrypt and did some benchmarks which show encryption and decryption
speeds of roughly 2GB/s.

Might this have something to do with the data alignment on disk? At
least with lvm it's suggested to define dataalignment=1m on SSD's. Is
it possible to define data alignment for dm-crypt?

Another possibility that would come to mind is a bug in the kernel.

I followed this guide to set up the encryption by the way:
https://wiki.archlinux.org/index.php/Dm-crypt_with_LUKS

Hoping to hear from you soon.

Kind regards

Joakim Reinert
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Re: [dm-crypt] Performance problems

[Milan Broz]

On 11/19/2012 12:51 PM, Joakim Reinert wrote:
> I have loaded the module aesni_intel and verified that the refcnt
> changes in /proc/crypto when i open/close the encrypted partition.

How exactly the storage stack looks like? Using underlying partition?
please paste lsblk output and cryptsetup luksDump
(you can remove slot info and hash, algorithm and payload offset
is important here)

Try to add oflag=direct to your dd command (for write) or iflag=direct
for read.

Yes, AES-NI should provide more than necessary performance.

> I've already harrassed everybody at #archlinux and #crypto in IRC but
> nobody seems to know what the problem might be. I also installed
> truecrypt and did some benchmarks which show encryption and decryption
> speeds of roughly 2GB/s.

Truecrypt by default use dm-crypt (if not switched off in config),
but internal benchmarks measure non-kernel services.


> Might this have something to do with the data alignment on disk? At
> least with lvm it's suggested to define dataalignment=1m on SSD's. Is
> it possible to define data alignment for dm-crypt?

1MiB alignment is default for LUKS (and for LVM as well btw), depends
on version and if underlying partition is aligned.

Need info above to check.

Milan