On Wed, Dec 04, 2002 at 08:59:35PM +0100, Russell Coker wrote: > I have some servers that are giving inadequate disk performance for Maildir > mail spools. They are running kernel 2.4.19 (2.4.20 upgrade is planned) and > 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 journalling > which should increase performance, but still probably won't give me enough. > So I am thinking of using an "external journal" (or using software RAID to > put the part of the partition containing the journal on a different device). > > The device containing the journal would be something much faster than physical > 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 > unexpected power outages of at least 24 hours duration, can commit a write in > less than 1ms, supports unlimited writes, and connects to a IDE or SCSI bus > (or PCI if there's a suitable Linux driver). Did you check out Micro Memory Inc? (http://www.umem.com/) I think they have some PCI-cards (with linux-drivers) which may be suitable for this. 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. -- Ragnar Kjørstad
