drive performance

[der.hans]

moin moin,

We're using SATA II ( 3.0 GB/s ) drives. Some of our servers consistently
have iowait issues. Those machines also can't tolerate drive search tools
such as find and du.

Looking at one that was having problems today. top is showing wait
constantly over 5% and up to 15%. It was stuck over 10% earlier today and
up to 50%. It's a dual-proc quad-core system.

iowait is showing write staying below 3 MB/s and currently mostly less
than 1 MB/s. Reads are almost non-existent.

Avg wait is jumping up to 800 ms, sometimes higher.

This machine is mostly only writing out MySQL changes and logs.

Should writing 3GB/s really cause a lot of io wait?

Hmm, I see the filesystem is not mounted noatime, changing that now.
Didn't immediately change io wait.

A java process is eating most of the 64GB of RAM, but the swap partition
is not showing any disk activity. The java process is tied to another disk
as well.

This machine does not have an SAS controller, but I am considering moving
to SAS for future machines, budget willing. We might just move to RAID 0
for the DB. The java proc is already writing to RAID 0 in most cases.

I'm going to run some iozone or bonnie++ checks on a similar machine that
has not yet deployed.

$sudo hdparm /dev/sda

/dev/sda:
  IO_support   =  0 (default 16-bit)
  readonly     =  0 (off)
  readahead    = 256 (on)
  geometry     = 19457/255/63, sectors = 312581808, start = 0

ciao,

der.hans
-- 
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