From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: NVRAM support Date: Fri, 10 Feb 2006 10:43:32 -0500 Message-ID: <43ECB4A4.6010005@tmr.com> References: <43EC5655.1060504@web.de> <20060210124204.GC28676@harddisk-recovery.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20060210124204.GC28676@harddisk-recovery.com> Sender: linux-raid-owner@vger.kernel.org To: Erik Mouw Cc: Mirko Benz , linux-raid@vger.kernel.org List-Id: linux-raid.ids Erik Mouw wrote: >On Fri, Feb 10, 2006 at 10:01:09AM +0100, Mirko Benz wrote: > > >>Does a high speed NVRAM device makes sense for Linux SW RAID? E.g. a PCI >>card that exports battery backed memory. >> >> > >Unless it's very large (i.e.: as large as one of your disks), it >doesn't make sense. It will probably break less often, but it doesn't >help you in case a disk really breaks. It also won't speed up an MD >device much. > > > >>Could that significantly improve write speed for RAID 5/6 (e.g. via an >>external journal, asynchronous operation and write caching)? >> >> > >You could use it for an external journal, or you could use it as a swap >device. > > Let me concur, I used external journal on SSD a decade ago with jfs (AIX). If you do a lot of operations which generate journal entries, file create, delete, etc, then it will double your performance in some cases. Otherwise it really doesn't help much, use as a swap device might be more helpful depending on your config. > > >>What changes would be required? >> >> > >None, ext3 supports external journals. Look for the -O option in the >mke2fs manual page. Using the NVRAM device as swap is not different >from a using "normal" swap partition. > > >Erik > > > -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979