[Beowulf] Slow RAID reads, no errors logged, why?

[Jonathan Engwall]

I am curious about such things.
The DELL specs show the 710 can handle 32 devices, while the 730 can handle
255! The
pdf spec sheet also says the h730 has "workload profiles." If you are
nowhere near 255 disks perhaps you can change the controller?

On Wed, Mar 21, 2018 at 9:21 AM, David Mathog <mathog at caltech.edu> wrote:

> On Tue, 20 Mar 2018 00:55:01 +0000  Jörg Saßmannshausen wrote:
>
> I am wondering if that is not what you would expect.
>> The long SMART test is quite thorough so the disc will be subject to
>> quite a
>> bit of stress. Thus, it could well be that the controller is slowing down
>> the
>> rest of the RAID as there is a bottle neck.
>>
>
> Long SMART tests are run on active RAID systems here all the time, this is
> the only machine so far where this massive slow down has been noted.  The
> others might slow down a few percent, but a drop in the read rate from
> ~400Mb/s to 30Mb/s is just horrible.  I'm wondering if the disks on this
> one system (the only machine here with this model disk) disable readahead
> or command queuing or something of that sort when a long SMART test runs.
> However, no change in the read ahead value is visible with "blockdev
> --report" with and without that SMART test running.  The disks are 2Tb
> 6.0Gb/s SAS with 128Mb cache and 4.16ms latency.
>
> Regards,
>
> David Mathog
> mathog at caltech.edu
> Manager, Sequence Analysis Facility, Biology Division, Caltech
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