Sebastian Kuzminsky <seb@xxxxxxxxxxx> wrote:
> Question 1: Why didnt the raid sync I/O show up with vmstat?
>
> Question 2: Why was it limited to 17 MB per second? The maximum was
> left at the default, 200 MB/s. The min was also at the default, 1 MB/s.
> I get 60 MB/s per disk with "hdparm -tT" (that's using one disk at a time,
> but still). The checksumming code does > 3 GB/s.
Some more info... vmstat doesnt see it, but "iostat -m" does:
avg-cpu: %user %nice %system %iowait %steal %idle
0.00 0.00 3.96 0.00 0.00 96.04
Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn
hda 0.00 0.00 0.00 0 0
hde 0.00 0.00 0.00 0 0
hdg 0.00 0.00 0.00 0 0
hdi 0.00 0.00 0.00 0 0
hdk 0.00 0.00 0.00 0 0
sda 201.00 18.06 8.56 18 8
sdb 184.00 18.06 8.62 18 8
sdc 209.00 18.06 8.59 18 8
sdd 151.00 17.16 9.00 17 9
md0 0.00 0.00 0.00 0 0
md1 0.00 0.00 0.00 0 0
hda is the system disk, hd[egik] are PATA disks that make up md0, and
sd[abcd] are SATA disks that make up md1. md0 is idle, md1 is syncing.
This all makes more sense now - it's only getting 18 MB/s because it's
spending all that time writing.
But wait, why is it only writing half as much as it reads? This is a
4-disk RAID-6, as I understand it, it should read 2 strips and write 2
strips per stripe.
--
Sebastian Kuzminsky
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