Lustre discuss - May 2006 - Stable performance from a one disk OST?

Magnus Karlsson wrote:
> 
> I have been using Lustre now for nearly a year, and the problem I have
> is kind of odd. For a number of reasons I desire to have a relatively
> stable performance (throughput and latency) from the file system. In
> all the releases since 0.6 I have noticed that I indeed get this when
> the majority of the files are in the memory of the OST, but not when
> they are on disk. Every 60 seconds kswapd suddenly swaps in 200-700
> pages and the throughput drops an order of a magnitude and the latency
> shoots up an order of magnitude for a second or two. Do you know how I
> could alleviate this behavior?
Over the last two years we have seen countless strange behaviours from
the Linux VM.  I can''t say for sure whether we have seen this
particular
one.

We do have one patch, which can probably be included in 1.0.3, which
will let you turn off the OST''s read cache by flipping a bit in /proc.
I would be curious to hear if this resolves your issue.

Can you try again after 1.0.3 and get back to us?

Thanks--

-Phil

Hi,

I have been using Lustre now for nearly a year, and the problem I have
is kind of odd. For a number of reasons I desire to have a relatively
stable performance (throughput and latency) from the file system. In
all the releases since 0.6 I have noticed that I indeed get this when
the majority of the files are in the memory of the OST, but not when
they are on disk. Every 60 seconds kswapd suddenly swaps in 200-700
pages and the throughput drops an order of a magnitude and the latency
shoots up an order of magnitude for a second or two. Do you know how I
could alleviate this behavior?

Here are my system details: Lustre 1.0.1 on your standard 2.4.20
kernel rpm. The OST is running on a box with 2 1GHz P3 processors and
with 2G of memory. There is only one UltraSCSI2 HP disk drive
connected to the system. The load I generate using iozone is of one
thread sequentially reading a file (in 64K chunks) that is larger than
2G (so that it will be on disk).

One possible solution I could use as a last resort is to buy
one extra HD for every single box that I have, and then have the
Lustre file system data on one, and RedHat on the other. I would be
great if somebody could suggest something cheaper ;-).

BTW, Lustre has come a long way in a year. The 1.0 release is really
good. Congratulations.

Thanks: Magnus Karlsson