non volatile ram devices
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. At this stage it is impossible for me to replace disks, RAID controllers, or anything else really significant. 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. I have been doing some research on non-volatile memory devices. I only found one company producing disks that are RAM based with battery backup, and they seem to start at $10K (too expensive - probably because they are much larger than I need, I need 128M at most, they provide 2G). I found many companies selling flash memory, but that only takes a million writes (that'll last about an hour for the use I plan). I found one company selling PC-Card devices that have two batterys for backup, but that requires getting a PCI controller for PC-Card's (something I haven't tried before). 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). -- http://www.coker.com.au/selinux/ My NSA Security Enhanced Linux packages http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark http://www.coker.com.au/postal/Postal SMTP/POP benchmark http://www.coker.com.au/~russell/ My home page
Re: non volatile ram devices
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
Re: non volatile ram devices
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. At this stage it is impossible for me to replace disks, RAID controllers, or anything else really significant. 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. I have been doing some research on non-volatile memory devices. I only found one company producing disks that are RAM based with battery backup, and they seem to start at $10K (too expensive - probably because they are much larger than I need, I need 128M at most, they provide 2G). I found many companies selling flash memory, but that only takes a million writes (that'll last about an hour for the use I plan). I found one company selling PC-Card devices that have two batterys for backup, but that requires getting a PCI controller for PC-Card's (something I haven't tried before). 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). The umem.com folks sell a device that we have tested and benchmarked reiserfs on. If I could get Edward to format benchmarks in a way that conveys that information that is relevant to persons reading them, I would post them on our mailing list Hans
Re: non volatile ram devices
Hello! 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. May I ask what kind of inadequacy on what kinds of operations do you observe? Thank you. Bye, Oleg
