A little RAID experiment

[Stefan Ring]

> Read 0b  Written 995.77Mb  Total transferred 995.77Mb  (66.337Mb/sec)
>  8491.11 Requests/sec executed]

I was a bit sceptical towards your measurement at first, especially
since your xfs_bmap shows that the file is split into 4 regions which
nicely aligns (almost) with the agcount=4 setup that the benchmark
emulates, but this seems to be just a coincidence.

Meanwhile, I've found a customer's system, where we have a MegaRAID
SAS 1078 with a 6-disk RAID 6 volume, and this one delivers 54MB/sec,
which really puts the SmartArray controller to shame at its measly
4MB/sec.

I just want to stress that our machine with the SmartArray controller
is not a cheap old dusty leftover, but a recently-bought (December
2011) not exactly cheap Blade server, and that’s all you get from HP.