[GLLUG] Odd SATA Issue - slightly OT

Ken Smith kens at kensnet.org
Sat Dec 29 11:35:23 UTC 2018

Ken Smith via GLLUG wrote:
> Ken Smith via GLLUG wrote:
>> Alain D D Williams via GLLUG wrote:
>>> On Mon, Dec 24, 2018 at 08:51:09PM +0000, Greater London Linux UUG 
>>> wrote:
>>>> Hi Everyone,
>>>> I have an older centos 6 system that has 3 sata disks in soft raid5.
>>>> I've noticed that the disk performance has become very poor.
>>>> I did several "dd if=/dev/sdX of=/dev/null count=10000" tests on the
>>>> disks and found one of them performing around 1 MB/s while the
>>>> others are at 150 MB/s or more.
>>> A cheat fix attempt is to replace the power supply. These tend to 
>>> fade over time
>>> and can cause disks to play up - however I would have expected to 
>>> see errors in
>>> /var/log/messages
>> Thanks Alain, I hadn't thought of that. I'll measure some voltages 
>> first and see what I get.
>> :-) Ken
> I monitor the voltages and fan speeds, among other things,  with 
> Zabbix. Something definitely happened about 10 days ago according to 
> the Zabbix records. Thanks :-) Ken
PSU voltages looked good but swapped it and the Motherboard (I have a 
spare) & sata cable but sadly no change. Have added a spare disk and 
done some mdadm juggling to introduce the new disk and fail the suspect 
one. Once the raid had rebuilt the performance is back to normal.

/boot & Grub loader are on the suspect disk. Have already copied /boot 
to the new disk but need to reinstall the boot loader on that disk and 
update fstab with the new /boot.

Strange that a WD NAS disk can work fine except 100x slower than normal. 
iostat -x was showing huge values for await on that WD device.

Oh well - chalk that down to experience.

:-) Ken

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