If I use --assume-clean in mdadm, I see performance is 10-15% lower as compared to the case wherein this option is not specified. When I run without --assume_clean, I wait until mdadm prints "recovery_done" and then run IO benchmarks... Is perf drop expected? Thanks. On Mon, Apr 11, 2011 at 3:18 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Mon, 11 Apr 2011 10:53:55 +0100 Robin Hill <robin@xxxxxxxxxxxxxxx> wrote: > >> On Mon Apr 11, 2011 at 02:36:50AM -0700, Linux Raid Study wrote: >> > On Mon, Apr 11, 2011 at 2:25 AM, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote: >> > > On Mon Apr 11, 2011 at 01:32:34 -0700, Linux Raid Study wrote: >> > >> On Sat, Apr 9, 2011 at 1:50 AM, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote: >> > >> > On Fri Apr 08, 2011 at 05:40:46PM -0700, Linux Raid Study wrote: >> > >> > >> > >> >> What I'm not sure of is if the device is newly formatted, would raid >> > >> >> recovery happen? What else could explain difference in the first run >> > >> >> of IO benchmark? >> > >> >> >> > >> > When an array is first created, it's created in a degraded state - this >> > >> > is the simplest way to make it available to the user instantly. The >> > >> > final drive(s) are then automatically rebuilt, calculating the >> > >> > parity/data information as normal for recovering a drive. >> > >> > >> > >> Thanks. So, the uneven (unequal) distribution of Wrtie/Sec numbers in >> > >> the iostat output are ok...is that correct? >> > >> >> > > If it hadn't completed the initial recovery, yes. ÂIf it _had_ completed >> > > the initial recovery then I'd expect writes to be balanced (barring >> > > any differences in hardware). >> > > >> > The initial recovery should normally be done during first few minutes >> > .... this is a newly formatted disk so there isn't any user data >> > there. So, if I run the IO benchmark after say 3-4 min of doing, I >> > should be ok? >> > >> > mdam --create /dev/md0 --raid5.... >> > mount /dev/md0 /mnt/raid >> > mkfs.ext4 /mnt/raid >> > >> > ...wait 3-4 min >> > >> > run IO benchmark... >> > >> > Am I correct? >> > >> No, depending on the size of the drives, the initial recovery can take >> hours or even days. For RAID5 with N drives, it needs to read the >> entirity of (N-1) drives, and write the entirity of the remaining drive >> (whether there's any data or not, the initial state of the drives is >> unknown so parity data has to be calculated for the entire array). >> >> Check /proc/mdstat and wait until the array has completed resync before >> running any benchmarks. > > or run > Âmdadm --wait /dev/md0 > > or create the array with --assume-clean. ÂBut if the array is raid5, don't > trust the data if a device fails: Âuse this only for testing. > > NeilBrown > > >> >> Cheers, >> Â Â Robin > > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
