Hello

Our LAMP application is showing I/O latency. I was wondering if we
could move to multiple Apache servers, each connected through their
own disk controller to a single, shared RAID0 bay?

Our hoster recommends that we use a NAS, but I'm concerned about
network + NFS latency.

Thank you for any tip.

Gilles Ganault wrote:
> Hello
>
> Our LAMP application is showing I/O latency. I was wondering if we
> could move to multiple Apache servers, each connected through their
> own disk controller to a single, shared RAID0 bay?
>
> Our hoster recommends that we use a NAS, but I'm concerned about
> network + NFS latency.
>
> Thank you for any tip.

Where's the latency being seen? Between the user and the application or
from the application to the storage? If you have latency from the
application (mysql/apache) to the storage then higher performance
storage is needed - more disks and/or more cache - regardless of the
number of servers.

If you need several servers accessing the same dataset and it's largely
reads, NFS is the easiest way. If you want to directly connect several
servers to the same storage you'll need a storage controller which
allows multiple devices to access the storage and you'll need to install
a cluster filesystem. That's a load of complexity that you could
probably do without.

If you have a dedicated network, then the latency of NFS & the network
is going to be insignificant compared to the latency of a disk access.

Pete

Gilles Ganault wrote:
> Hello
>
> Our LAMP application is showing I/O latency. I was wondering if we
> could move to multiple Apache servers, each connected through their
> own disk controller to a single, shared RAID0 bay?
>
> Our hoster recommends that we use a NAS, but I'm concerned about
> network + NFS latency.
>
> Thank you for any tip.

You sound confused about all this.

What is the problem you're experiencing, or how did you arrive at "showing
I/O latency" as the bottlneck in this case?

On Mon, 25 Aug 2008 12:15:01 GMT, Pete
wrote:
>Where's the latency being seen? Between the user and the application or
>from the application to the storage?

Thanks guys for the input.

It was between the www servers and the MySQL + JPGs server. We asked
the hoster to add a filer, and performance is much better now, with
the filter being shared between two Apache servers

If demande keeps rising, I guess we'll have to investigate MySQL
clusters, so that the DB doesn't become the bottleneck again.

> If you want to directly connect several servers to the same storage
> you'll need a storage controller which allows multiple devices
> to access the storage and you'll need to install a cluster filesystem.
> That's a load of complexity that you could probably do without.

Yes, that's what I suspected :-/ So I guess the standard solution to
scaling databases is to add some kind of load balancer, and 2 or more
DB servers behind it.

Gilles Ganault wrote:
> On Mon, 25 Aug 2008 12:15:01 GMT, Pete
> wrote:
>>Where's the latency being seen? Between the user and the application or
>>from the application to the storage?
>
> Thanks guys for the input.
>
> It was between the www servers and the MySQL + JPGs server. We asked
> the hoster to add a filer, and performance is much better now, with
> the filter being shared between two Apache servers
>
> If demande keeps rising, I guess we'll have to investigate MySQL
> clusters, so that the DB doesn't become the bottleneck again.
>
>> If you want to directly connect several servers to the same storage
>> you'll need a storage controller which allows multiple devices
>> to access the storage and you'll need to install a cluster filesystem.
>> That's a load of complexity that you could probably do without.
>
> Yes, that's what I suspected :-/ So I guess the standard solution to
> scaling databases is to add some kind of load balancer, and 2 or more
> DB servers behind it.

It's really to tune things first, then as a last resort, start adding more
hardware. More hardware and more layers is always harder to manage.

As junior as mysql is, there's lots of stuff that can be tweaked. The
apps using it should be examined as well if you are running into
performance problems.

On Wed, 27 Aug 2008 20:45:11 +0000 (UTC), Cydrome Leader
wrote:
>It's really to tune things first, then as a last resort, start adding more
>hardware. More hardware and more layers is always harder to manage.

I'll make sure MySQL + queries are configured as best as possible.
Thanks.