From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?iso-8859-1?Q?Ragnar_Kj=F8rstad?= Subject: Re: non volatile ram devices Date: Wed, 4 Dec 2002 21:24:47 +0100 Message-ID: <20021204212447.C20004@vestdata.no> References: <200212042059.35300.russell@coker.com.au> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com Content-Disposition: inline In-Reply-To: <200212042059.35300.russell@coker.com.au>; from russell@coker.com.au on Wed, Dec 04, 2002 at 08:59:35PM +0100 List-Id: Content-Type: text/plain; charset="iso-8859-1" To: Russell Coker Cc: linux-ide-arrays@lists.math.uh.edu, ReiserFS On Wed, Dec 04, 2002 at 08:59:35PM +0100, Russell Coker wrote: > I have some servers that are giving inadequate disk performance for Maild= ir=20 > mail spools. They are running kernel 2.4.19 (2.4.20 upgrade is planned) = and=20 > using ReiserFS for everything that's important. One thing you might considder is replacing the reiserfs hash with a maildir-specific hash. In my rather limited testing I found that it was significantly faster; I think some tests gave 200-300% speed improvement. But, as I said, there was only limited testing. Don't go this route unless you have the time to test it properly both for stability and performance. > What I am thinking of doing is using a kernel that supports data journall= ing=20 > which should increase performance, but still probably won't give me enoug= h. =20 > So I am thinking of using an "external journal" (or using software RAID t= o=20 > put the part of the partition containing the journal on a different devic= e). >=20 > The device containing the journal would be something much faster than phy= sical=20 > media. Even if the device is just a regular disk it should give you a real performance boost. Depending on your RAID-setup, it may not be the throughput, but the seeking back and forth between the journal and the rest of the disk that kills performance. Having the journal on a seperate disk solves that problem. > Does anyone know of an affordable ($1000 or less) device that can survive= =20 > unexpected power outages of at least 24 hours duration, can commit a writ= e in=20 > less than 1ms, supports unlimited writes, and connects to a IDE or SCSI b= us=20 > (or PCI if there's a suitable Linux driver). Did you check out Micro Memory Inc? (http://www.umem.com/)=20 I think they have some PCI-cards (with linux-drivers) which may be suitable for this.=20 However, the main strength of flash/RAM devices is that you can do random writes very fast. For a journal deice all access will be sequential, so there may not be much advantage compared to using a seperate disk for the journal? I've never tried, so I'm not sure exactly how well it would work. Is your server read- or write- bound? I've found that some mailservers are IO-bound because of reads (I guess pop- and imap-servers that are polling), and then the external journal is not likely to help. --=20 Ragnar Kj=F8rstad