Messages in this thread | | | Date | Sat, 25 Jan 2003 05:41:47 +1100 | From | Nick Piggin <> | Subject | Re: 2.5.59mm5, raid1 resync speed regression. |
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David Mansfield wrote:
>>David Mansfield wrote: >> >> >>>Hi Andrew, list, >>> >>>I'm booting 2.5.59mm5 to run a database workload benchmark that I've been >>>running against various kernels. I'll post those results if they are >>>interesting later, but I did notice that the raid1 resync is proceeding at >>>half the speed (at best) that it usually does (vs. 2.5.59 that is). >>> >>>It currently at about 4-8 mb/sec (and falling as resync progresses), >>>usually at 12-15 mb/sec. >>> >>>System is SMP 2xPIII 866mhz, 2GB ram, raid1 is two 15k U160 (running only >>>an Ultra speed :-( because the onboard controller sucks) SCSI disks, same >>>channel on aic7xxx. >>> >>>Kernel is 2.5.59-mm5 compiled with gcc version 2.96 20000731 (Red Hat >>>Linux 7.3 2.96-112) >>> >>>David >>> >>> >>Thanks for the report. Please do post any results you get. >> >>What disk workload exactly does a RAID1 resync consist of? >> >> > >Well, I don't know the internals of it, but it goes something like: > >decide which half of the mirror is more current. Read blocks from this >partition, write to other. Periodically update raid-superblock or >something. The partitions in my case are on separate SCSI disks. > >The thing about it is, it attempts to throttle the sync speed to not >interfere too much with operation of the system (background resync could >suck up all i/o 'cycles' and make a system unusable) by monitoring the >amount of requests through the raid device itself. The sysadmin can set a >'speed limit' in /proc to control this, but I have it really high, so it >*should* be syncing at max speed regardless of any i/o happening to the >raid device itself. > >So it's a bit complicated. You'd have to look at the code or ask someone >(Neil Brown) who knows more about it. > >.... I'm rebooting and looking at it again. Here's something strange, if >I let the system sit completely idle, the resync speed increases almost to >the 'normal' rate, but causing any (minor) disk activity in another window >causes the rate to plummet for minutes. > >I think there's some strange interaction with the speed-limit code in the >raid1 resync. > Perhaps. I think there is something up with request expiry that might cause a disk to choke up like this. Especially writes. I'll fix that over the weekend if I can.
> > >David > >P.S. I'll post my benchmark date if/when available. > > > >
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