I am using dmcrypt/LUKS on: CentOS 5.5 kernel 2.6.18-194.32.1.el5 MySQL 5.5.12 cryptsetup-luks 1.0.3 ext3 Doing a mysqldump from the LUKS/dmcrypt volume takes twice as long as it does from a non-encrypted volume. Only a few percent of the CPU are taken for the encryption so it isn't kcryptd maxing out the CPU. Most interestingly I notice that iowait goes from 90% for the non-encrypted db to 99% for the encrypted db. It really looks like a lot more IO is somehow generated. This makes no sense to me as I understand dmcrypt to sit above the disk layer and do a block-for-block encrypt/decrypt of the data as it passes through. How could it possibly cause extra disk IO? At first I thought maybe it was disk alignment (which has bitten me many times before) but we are doing reads here, not writes. iostat confirms that during the mysqldump practically no writes are happening. I've also looked at increasing readahead to no effect. I've googled and found that as long as dmcrypt isn't maxing out the CPU (for which latest kernels support AES-NI and multi-threaded kcryptd) the performance with and without encryption should be pretty much the same. I don't understand why my reads are taking such a hit. Any ideas? -- Tracy Reed _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
