[OpenIndiana-discuss] Recommendations for fast storage

[Jim Klimov]

On 2013-04-16 20:30, Jay Heyl wrote:
> What would be the logic behind mirrored SSD arrays? With spinning platters
> the mirrors improve performance by allowing the fastest of the mirrors to
> respond to a particular command to be the one that defines throughput. With

Well, to think up a rationale: it is quite possible to saturate a bus
or an HBA with SSDs, leading to increased latency in case of intense
IO just because some tasks (data packets) are waiting in queue waiting
for the bottleneck to dissolve. If another side of the mirror has a
different connection (another HBA, another PCI bus) then IOs can go
there - increasing overall performance.

Basically, this answer stems from logic which applies to "why would we
need 6Gbit/s on HDDs?" Indeed, HDDs won't likely saturate their buses
with even sequential reads. The link speed really applies to the bursts
of IO between the system and HDD's caches. Double bus speed roughly
halves the time a HDD needs to keep the bus busy for its portion of IO.
And when there are hundreds of disks sharing a resource (an expander
for example), this begins to matter.

HTH,
//Jim Klimob