[CentOS] Slow RAID Check/high %iowait during check after updgrade from CentOS 6.5 -> CentOS 7.2

[Kelly Lesperance]

Software RAID 10.  Servers are HP DL380 Gen 8s, with 12x4 TB 7200 RPM drives.

On 2016-06-01, 3:52 PM, "centos-bounces at centos.org on behalf of m.roth at 5-cent.us" <centos-bounces at centos.org on behalf of m.roth at 5-cent.us> wrote:

>Kelly Lesperance wrote:
>> I did some additional testing - I stopped Kafka on the host, and kicked
>> off a disk check, and it ran at the expected speed overnight. I started
>> kafka this morning, and the raid check's speed immediately dropped down to
>> ~2000K/Sec.
>>
>> I then enabled the write-back cache on the drives (hdparm -W1 /dev/sd*).
>> The raid check is now running between 100000K/Sec and 200000K/Sec, and has
>> been for several hours (it fluctuates, but seems to stay within that
>> range). Write-back cache is NOT enabled for the drives on the hosts we
>> haven't upgraded yet, but the speeds are similar (I kicked off a raid
>> check on one of our CentOS 6 hosts as well, the window seems to be 150000
>> - 200000K/Sec on that host).
><snip>
>Perhaps I missed where you answered this: is this software RAID, or
>hardware? And I think you said you're upgrading existing boxes?
>
>      mark
>
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