[ale] Performance issue

[Jim Kinney]

No jumpers that I can recall. All the sas jumpers only limit the size of
the addressable drive space and all of these show as full size.

On Aug 21, 2016 4:03 PM, "Jeff Hubbs" <jhubbslist at att.net> wrote:

> Are you sure none of the drives are jumpered out-of-the-box for a lower
> speed? That happened to me a few years back; caught it before I sledded the
> drives.
>
> On 8/21/16 11:06 AM, Jim Kinney wrote:
>
> Yep. 6Gbps is the interface. But even at a paltry 100Mbps actual IO to the
> rust layer, the 12 disk raid 6 array should _easily_ be able to hit 1Gbps
> of data IO plus control bits. The 38 disk array should hit nearly 4Gbps.
>
> The drives are Toshiba, Seagate and HGST. They all are rated for rw in the
> 230-260 MBps sustained (SATA can only do bursts at those rates) so 1.8 Gbps
> actual data to the platters.
>
> I'm expecting a sustained 15Gbps on the smaller array and 48Gbps on the
> larger. My hardware limits are at the PCIe bus. All interconnects are rated
> for 24Gbps for each quad-channel connector. It really looks like a kernel
> issue as there seems to be waits between rw ops.
>
> Yeah. I work in a currently non-standard Linux field. Except that Linux
> _is_ what's always used in the HPC, big-data arena. Fun!  ;-)
>
> I don't buy brand name storage arrays due to budget. I've been able to
> build out storage for under 50% of their cost (including my time) and get
> matching performance (until now).
>
> On Aug 21, 2016 10:04 AM, "DJ-Pfulio" <DJPfulio at jdpfu.com> wrote:
>
>> On 08/20/2016 10:00 PM, Jim Kinney wrote:
>> > 6Gbps SAS. 12 in one array and 38 in another. It should saturate the
>> bus.
>>
>> 6Gbps is the interface speed. No spinning disks can push that much data
>> to my knowledge - even SAS - without SSD caching/hybrids. Even then,
>> 2Gbps would be my highest guess at the real-world performance (probably
>> much lower in reality).
>>
>> http://www.tomsitpro.com/articles/best-enterprise-hard-drives,2-981.html
>>
>> You work in a highly specialized area, but most places would avoid
>> striping more than 8 devices for maintainability considerations. Larger
>> stripes don't provide much more throughput and greatly increase issues
>> when something bad happens.  In most companies I've worked, 4 disk
>> stripes were used as the default since it provides 80% of the
>> theoretical performance gains that any striping can offer.  That was the
>> theory at the time.
>>
>> Plus many non-cheap arrays will have RAM for caching which can limit
>> actual disks being touched. Since you didn't mention EMC/Netapp/HDS, I
>> assumed those weren't being used.
>>
>> Of course, enterprise SSDs changed all this, but would be cost
>> prohibitive at the sizes you've described (for most projects).  I do
>> know a few companies which run all their internal VMs on RAID10 SSDs and
>> would never go back. They aren't doing "big data."
>>
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>
>
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