Re: [squid-users] cache size and structure

> Riccardo Castellani wrote:
>> I'm preparing new squid machine and I'm defining cache size.
>> Old squid had 2 entries into "cache_dir directive" :
>>
>> cache_dir ufs /usr/local/cache/1 3500 128 256
>> cache_dir ufs /usr/local/cache/2 2500 128 256

On 23.06.09 13:07, Chris Robertson wrote:
> I'd strongly suggest using "aufs" instead of "ufs".

seconded.

>> My cache traffic volume (I/O) is about 2 Mbps a week with peaks of 3 Mbps.

ehm, 2 megabits per socond "a week"?

>> This squid cache is the parent of 2 other squid machines and it gives
>> answers to about 1000 users.
>>
>> 1- I read you suggest 1 cache_dir to same partition, why I can't use 2
>> folder in tha same partition ?!

> You can, but why would you want to? The suggestion is one cache_dir per
> spindle to spread the IO load. Putting multiple partitions on one
> spindle makes about the same sense as multiple cache_dirs in the same
> partition. Access to all of them will be contending for the limited IO
> resources available.

That means, different cache_dirs are mostly for using different disks.
Or different storage schema, e.g. using COSS (which is perfect for small
files) in addition to *ufs

>> 2- What do you think my caches size ? 3500 and 2550 ?
>
> Depends on your memory load. A larger cache leads to storing more
> objects, which requires more memory to track. The suggestion I recall
> is "a week's worth of traffic". If you are seeing an average of 2Mbit/s
> 24 hours a day, seven days a week, that would lead to a cache of around
> 150GB.

I'd say it depends on disk load also :) caching one-two weeks of HTTP
traffic is not that good if disk becomes the leak. But switching to one
aufs cache_dir (plus optional COSS) should give enough of speed benefits so
the cache could be increased.

If users acess your squid directly (not only through child proxies), there
may be the need for cache_mem.

See please squid FAQ for informacions about memory usage...
http://wiki.squid-cache.org/SquidFaq/SquidMemory

>> and its directory structure (128,256) ?!

> This is entirely dependent on the filesystem you are using and the
> number of objects you cache. The goal is to keep the number of files
> per directory reasonable, because most filesystems are not optimized for
> a "large" ratio (10s of thousands of files per directory).

I have "48 256" for 20GiB cache. If you take the number of files in the
cache directory, divide by 256 (l2 dirs) and 256 (max files in l2 dir), you
should get the approximate need of l1 dirs. The average object size is
aropund 13KiB, which means, you should have one L1 cache_Dir per ~800MiB of
cache size. Splitting small files to COSS (using min-size option for *ufs
and max-size for COSS) will make that even smaller number, since only big
iles will be placed to *ufs directory hierarchy.

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