Re: SSD as Cache?

[basti <black.fledermaus@arcor.de>]

On 09.11.2013 02:19, David Christensen wrote:
> On 11/08/2013 12:12 PM, basti wrote:
>> Sorry,
>> /sbin/udevadm info --query=property --name=sdb |grep ID_MODEL
>> ID_MODEL=M4-CT128M4SSD2
>> MTBF 1,2 Mio h = 500000 days = 136,98 years
>> Drive Endurance 72TB=40GB per day for 5 years
>> I will try to measure the "traffic" next week.
>> There are Hosted Servers, they are changed every 2 years to "new
>> hardware".
>> Here are Dedicated Root Servers.
>> The Webapplication Files (PHP and so on are on RAID), also the Postgres
>> Data-Dir.
>> The Root Partition is on SSD, also /boot and swap.
>> The Images are on SSD, "mounted via bind".
>> The System has 32GB RAM and thats mainly used for Postgres cache and
>> MongoDB.
>> There is a Backend Postgres Database Server that cluster to this
>> Frontend Server.
>> So that this Frontend / Application Server can work "standalone".
>> The mongoDB "cache" the Postgres Querys and some json Objects for the
>> Application. Serialized Arrays and so on.
>> When this crash it doesn't matter, It only takes longer to display the
>> Webpages.
>> I think 20-30 GB will be free on SSD when it's used as Cache, even more.
>> (Thats my personal limit, that should be free on system disk.)
>
> Please don't top-post.
>
>
> Please trim included text.
>
>
> That's a non-trivial configuration.  I infer two physical machines and
> at least four services from the above.  Your "Images" statement makes
> me wonder if you are also running hypervisor(s).  Are you?
>
>
> Looking back to your original post:
>
> > Now I plan to improve the performance of my Webapplication.
> > The Cache is about 10.0 GB in 2000000 files.
> > Can this cache moved to SSD?
>
> Which cache are we talking about?
>
>
> Where is the cache currently?
>
>
> On 11/08/2013 03:46 PM, Karl E. Jorgensen wrote:
> > Standard practice for tuning is to make measurements first.
> > If your measurements show that disk IO is your bottleneck, then yes:
> > SSD may help. But if your bottleneck is elsewhere, then changing
> > things in the disk subsystem is unlikely to have any effect.
>
> +1
>
>
> Do you have any measurements?
>
>
> David
>
>

There is a simple file-cache with serialized string/array elements of
the webapplication.
So it's faster to query the cache and deliver the serialized cache as
devery the side by php.

thanks for any help right now, I will try to store the cache in mongodb.