I only have 1gb RAM in my server currently, its mainly only storage, but I do run a sabnzbd server on it, but it doesn't unrar anything, only sfv checking and the occasional par repair..

 

Anyway, I've been reading a little bit into caching dirs, and I'm wondering if 1gb is enough to cache a lot of folders.. I don't know an exact count off hand, but it's probably in the neighborhood of <10k directories including root folders and all subfolders..

 

Also, how often are the directories cached? If I delete a folder and the hdd spins down, will that folder still show for x amount of time?

I would not run cache_dirs  with only 1GB if you are running the other application.

 

cache_dirs will use low memory, but low memory will be at a premium for the root filesystem (initramfs), md driver buffers, buffer cache, emhttp and other applications. See my point?

 

cache_dirs may in fact prevent spindown or may cause premature spin up.

 

if you were to bump your ram to 2gb-4gb then cache_dirs may be more effective.

 

>  If I delete a folder and the hdd spins down, will that folder still show for x amount of time?

Once the directory is removed, it is removed.

I only have 1gb RAM in my server currently, its mainly only storage, but I do run a sabnzbd server on it, but it doesn't unrar anything, only sfv checking and the occasional par repair..

 

Anyway, I've been reading a little bit into caching dirs, and I'm wondering if 1gb is enough to cache a lot of folders..

I have 512 Meg of RAM in my server.  Works for me.

I don't know an exact count off hand, but it's probably in the neighborhood of <10k directories including root folders and all subfolders..

I've got just under 9000.

Also, how often are the directories cached? If I delete a folder and the hdd spins down, will that folder still show for x amount of time?

The scan rate is dynamic and auto adjusts.  Typically it is between every 5 and 10 seconds.  The goal is to keep the directory entries from being the least recently used disk blocks (and therefore not re-used by the buffer cache)

 

They will stay in the buffer cache forever with all disks spun down.

 

If we theorize every directory requires 100 bytes of "data" being cached, then 10,000  directories * 100 bytes = 1,000,000 bytes  (1 megabyte). 

 

You have plenty of memory to keep your directory entries cached.

(one megabyte of RAM)

There's a hash table in low kernel memory and if low memory is exhausted you will get an out of memory error.  It's not just 1MB, there is a hash table and other filesystem structures that are cached.

 

In addition the sabnzbd is going to be running, this will compete for space on initramfs and ram to run the application. Then the data it downloads gets put into the buffer cache.

 

I can tell you in my setup which has way more files, cache_dirs or any similiar process , kept disks from spinning down and often caused me to run out of memory. low kernel memory, which then causes the kernel to start killing processes.

 

In comparison I have 8GB ram and hundreds of thousands of files, so of course it will not work for me.

Even expanding the dentry cache table did not work. It got better, but I also would run out of ram faster if I did too much work on the server.  This is where you may see your issues. It may work for a while then when you start doing any form of work, the kernel will start to kill processes.

 

For 10,000 files/folders you may be just fine, but when you start running the par tool, it starts using memory. I've crashed my server a few times running par2 on large file sets.

 

I would say fire it up, test it out and kick the tires, watch the drive spin downs and spin ups and watch for out of memory/killing process messages.

 

If you never get any of these conditions, you are golden.

If you have a hint of these processes disappearing or out of memory errors you will need more ram.

thanks for the replies. i've started running cache_dirs and it seems to be working OK.. i downloaded a couple older/incomplete nzb's to see how it deals with repairing, and so far so good.. but i will make a point to upgrade my RAM some time in the near future, but for now it looks like 1GB is fine.

See this thread.

http://lime-technology.com/forum/index.php?topic=15729.msg146423#msg146423