OK, I've done some more testing on our IDE drive machine. First, some background. The hard drives we're using are Seagate drives, model number ST380023A. Firmware version is 3.33. The machine they are in is running RH9. The setup string I'm feeding them on startup right now is: hdparm -c3 -f -W1 /dev/hdx
where: -c3 sets I/O to 32 bit w/sync (uh huh, sure...) -f sets the drive to flush buffer cache on exit -W1 turns on write caching The drives come up using DMA. turning unmask IRQ on / off has no affect on the tests I've been performaing. Without the -f switch, data corruption due to sudden power down is an almost certain. Running 'pgbench -c 5 -t 1000000' and pulling the plug will result in recovery failing with the typical invalid page type messages. the pgbench database was originally set to -s 1 when initializing. If I turn off write caching (-W0) then the data is coherent no matter how many concurrents I'm running, but performance is abysmal (drops from ~ 200 tps down to 45, 10 if I'm using /dev/md0, a mirror set.) This is all on a single drive. If I use -W1 and -f, then I get corruption on about every 4th test or so if the number of parallel beaters is 50 or so. If I crank it up to 200 or increase the size of the database by using -s 10 during initilization. Note that EITHER a larger test database OR a larger number of clients seems to increase the chance of corruption. I'm guessing that the with -W1 and -f, what's happening is that at lower levels of parallel access, or a larger data set, the time between when the drive reports and fsync and when it actually writes the data out is climbing, and it is more likely that data that is in transit to the wal is getting lost during the power plug pull. Tom, you had mentioned adding a delay of some kind to the fsync logic, and I'd be more than willing to try out any patch you'd like to toss out to me to see if we can get a semi-stable behaviour out of IDE drives with the -W1 and -f switches turned on. As it is, the performance is quite good, and under low to medium loads, it seems to be capable of surviving the power plug being pulled, so I'm wondering if we can come up with a slight delay, that might drop the performance some small percentage while greatly decreasing the chance of data corruption. Is this worth looking into? I can see plenty of uses for a machine that runs on IDE for cost savings, while still providing a reasonable amount of data security in case of power failure, but I'm not sure if we can get rid of the problem completely or not. ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
