On 7/5/2013 8:33 PM, Christoph Anton Mitterer wrote: > One more on that, which I've just thought about: > > On Thu, 2013-07-04 at 18:07 -0400, Phil Turmel wrote: >> I believe dmcrypt is single-threaded, too. > Even if that is still true... and it with dmcrypt below MD it would run > with _one_ thread _per_ physical device... while the other way round > (dmcrypt on top of MD) it would run with _only one_ thread over the > _whole_ MD device (and thus also all disks)... > > ...would the former really give a performance benefit (or wouldn't it be > actually much worse). Yes. > Since even though you'd have one dmcrypt thread per disk now,... each of > them would have to en/decrypt the "same" actual data for different > devices... so while you have 4x threads... you need to do 4x > en/decryption works. This would only be true if using n-way mirroring. > Which wouldn't be the case when having dmcrypt on top of MD... sure > you'd only have one thread... You misunderstand the way this works. With striped md RAID each chunk goes to a different disk. All chunks contain dissimilar data. If you use dmcrypt at the lowest level of the stack you have one dmcrypt thread per chunk, each processing 1/n of the load. There is no duplication of work. -- Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
