From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Rees Subject: Re: Thoughts on using SSD Date: Thu, 26 Mar 2009 17:51:47 -0700 Message-ID: <72dbd3150903261751r911114ak16b2f9cd0d1da191@mail.gmail.com> References: <49CC0B0D.5000904@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49CC0B0D.5000904@tmr.com> Sender: linux-raid-owner@vger.kernel.org To: Bill Davidsen Cc: Linux RAID List-Id: linux-raid.ids On Thu, Mar 26, 2009 at 4:09 PM, Bill Davidsen wrote: > If I were to create a small raid device, raid1, made of the 4GB Ssd and 4GB > of SATA space, if I made the SATA write-mostly and write-behind, and put the > journal for my raid arrays (and bitmaps?) that seems likely to provide a > significant performance gain in small storage. > > Am I missing anything here? Is there an obvious drawback I'm missing? Yeah, the fact that it doesn't seem to be possible to take advantage of the write-behind feature? :-p Besides fsync, I think it may have something to do with barriers. As in, when you flush a barrier, that causes entire cache to get flushed to disk, including your write-behind disk. Hopefully Neil can chime in here. I found this thread from a while back which seemed relevant, but I haven't been able to digest the whole thing yet: http://lkml.org/lkml/2007/5/25/71 -Dave