Chris wrote: > Curious things to note here about md raid. When using encryption on top > of an device mapper device (md device), is inheritly slow and should > show no improvement for multiple threads doing encryption. Multiple > threads could only help improve speeds on multiple independent devices. I am not sure if I understand it correctly... If you create multiple encrypted devices, you have multiple threads now already. md is not device-mapper device, it is old raid device, but yes, it combines multiple disc into one block device, If there is running multiple IO on *one* device and they are independent we can encrypt/decrypt them in parallel - that should be implemented. (The problem is in order and synchronization.) > The device mapper creates an abstraction that pretends multiple > devices are one (for raid at least) so dm-crypt could not take advantage > of this due to block encryption. see above. > If you encrypt multiple raw devices > then make a device mapper on them, you would notice improvements in > speed. Unfortunately this doesn't work properly, it is an unstable > configuration (not sure why, I think both use the same area of the > device to store metadata). The md raid over multiple dm-crypt devices is strange configuration, I can imagine that there will be problem when some device fails. You need then not only to use mdadm to remove failed raid device, but also remove dm-crypt mapping for underlying device, it will not happen automatically. But in principle it should work. Milan -- mbroz@xxxxxxxxxx --------------------------------------------------------------------- dm-crypt mailing list - http://www.saout.de/misc/dm-crypt/ To unsubscribe, e-mail: dm-crypt-unsubscribe@xxxxxxxx For additional commands, e-mail: dm-crypt-help@xxxxxxxx
