Re: More testing: 4x parallel 2G writes, sequential reads

[Eric Sandeen <sandeen@redhat.com>]

Andreas Dilger wrote:

> The question is what the "best" result is for this kind of workload?
> In HPC applications the common case is that you will also have the data
> files read back in parallel instead of serially.

Agreed, I'm not trying to argue what's better or worse, I'm just seeing
what it's doing.

The main reason I did sequential reads back is that it more clearly
shows the file layout for each file on the graph.  :)  I'm just getting
a handle on how the allocations are going for various types of writes.

> The test shows ext4 finishing marginally faster in the write case, and
> marginally slower in the read case.  What happens if you have 4 parallel
> readers?

I'll test that a bit later (have to run now); I expect parallel readers
may go faster, since the blocks are interleaved, and it might be able to
suck them up pretty much in order across all 4 files.

I'd also like to test some of this under a single head, rather than on
HW raid...

-Eric