From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milan Broz Subject: Re: some general questions on RAID Date: Mon, 08 Jul 2013 07:25:53 +0200 Message-ID: <51DA4D61.2090708@gmail.com> References: <1372962602.8716.56.camel@heisenberg.scientia.net> <51D5F22C.70007@turmel.org> <51D9A7CF.6000700@gmail.com> <20130708145316.4486d0dc@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130708145316.4486d0dc@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Phil Turmel , Christoph Anton Mitterer , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/08/2013 06:53 AM, NeilBrown wrote: > On Sun, 07 Jul 2013 19:39:27 +0200 Milan Broz wrote: > > >> So if you have multiple IOs submitted in parallel from *different* CPUs, >> they are processed in parallel. >> >> If you have MD over dmcrypt, this can cause problem that MD sumbits all IOs >> with the same cpu context and dmcrypt cannot run it in parallel. > > For RAID1 and RAID10 this isn't true any more. > > Commit f54a9d0e59c4bea3db733921ca9147612a6f292c > in 3.6 changed this for RAID1 and a similar commit did for RAID10. > RAID4/5/6 still submit from a single thread as you say. Ah, sorry, missed that change, thanks Neil! So then it should perform much better. (But IIRC most reports about dmcrypt performance was either over high-speed SSD without AES-NI or over RAID5 - case like huge ftp archive where they need redundancy & offline data security. But here current design should be help...) Milan