[OpenAFS] Re: bonnie++ on OpenAFS

[Achim Gsell]

On Nov 23, 2010, at 12:15 AM, Simon Wilkinson wrote:

>=20
> On 22 Nov 2010, at 23:06, Achim Gsell wrote:
>>=20
>> 3.) But if I first open 8 files and - after this is done - start =
writing to these files sequentially, the problem occurs. The difference =
to 1.) and 2.) is, that I have these 8 open files while the test is =
running. This simulates the "putc-test" of bonnie++ more or less:
>=20
> AFS is a write-on-close filesystem, so holding all of these files open =
means that it is trying really hard not to flush any data back to the =
fileserver. However, at some point the cache fills, and it has to start =
writing data back. In 1.4, we make some really bad choices about which =
data to write back, and so we end up thrashing the cache. With Marc =
Dionne's work in 1.5, we at least have the ability to make better =
choices, but nobody has really looked in detail at what happens when the =
cache fills, as the best solution is to avoid it happening in the first =
place!

Sounds reasonable. But I have the same problem with a 9GB disk-cache, a =
1GB disk-cache, 1GB mem-cache and a 256kB mem-cache: I can write 6 GB =
pretty fast then performance drops to < 3MB/s ...

So long

Achim