From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: cpu/memory use Date: Thu, 20 Jan 2011 12:29:17 +1100 Message-ID: <20110120122917.3eb0a888@notabene.brown> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Roberto Spadim Cc: Linux-RAID List-Id: linux-raid.ids On Wed, 19 Jan 2011 22:14:45 -0200 Roberto Spadim wrote: > Hi, i wass thinking about cpu/memory use > i have a dual (three four) cpu > could i make linux to only use cpu1 for raid? and others to anythink > else, don=B4t migrate raid between cpus... and don=B4t allow others > programs to use raid cpu... > is it possible? > is it dificult? > it=B4s more linux related feature, not raid related, but could we imp= lement it? > what about memory usage? how many memory software raid use? is it per > device, per raid, does it have a hard limit (offcourse)? could we > calculate it? for example i want raid1 with two disks of 1tb, how man= y > memory should i buy? >=20 =46or levels other than RAID4/5/6, md/raid does not use any significant= amount of CPU or memory. =46or RAID4/5/6, md's use for CPU is single-threads so it will only use= a single CPU - which ever one the scheduler allocates it to from time to = time. The only room for improvement that I can see would be to allow the 'xor= ' calculation to be run in parallel on multiple CPUs and that would only = help if the storage devices were nearly as fast as a CPU. Where we have tri= ed parallelising xor, it has only made things slower.=20 =46or your particular question about RAID1 - use a RAID1 across two dev= ices would use less than 100K more than using just one of the devices. During resync it might use as much as a couple of megabytes of extra me= mory. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html