From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aryeh Gregor Subject: Re: It is possible to put write cache on ssd? Date: Wed, 9 Jun 2010 12:21:29 -0400 Message-ID: References: <4C0D44FC.8020908@tmr.com> <4C0F75B8.7020306@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <4C0F75B8.7020306@shiftmail.org> Sender: linux-raid-owner@vger.kernel.org To: MRK Cc: CoolCold , Mario , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, Jun 9, 2010 at 7:06 AM, MRK wrote: > Same problem with write-mostly/write-behind I think. I don't know how long > is the queue that holds data already committed to the SSD and not yet > committed to the HDD but it can't be too long. I'm reading the "man md" > right now and it's not extremely clear on this. I have the impression the > queue between the two it's either the /sys/block/hdddevice/queue/nr_requests > or it uses the write-intent bitmap (if set). In case of the nr_requests, > it's gonna be very short so the SSD can give you quick bursts but continuous > performance will be that of the HDD. I tried this once and posted some bonnie++ results: https://kerneltrap.org/mailarchive/linux-raid/2010/1/31/6742263