I have recently got iStat Server running on my unraid server allowing me to monitor my rig via my iphone. It is handly to have the basic monitoring statistics neatly displayed on one view. During my weekly back from my unraid server to another file server, I noticed that the 2GB RAM that I have was occupied almost ny half with Cached memory.

When the server initialled booted up, the Cached memory figure was only about 50 ~ 100MB, but while it was transferring file differences from itself onto the other file server, it peaked and stayed about 1GB. This stayed at this for the rest of the time that my server was online (powered on).

The questions I raise, what exactly is Cached memory? Is it like a buffer in which data is temporarily stored into RAM before it that either gets written onto the disk(s) or exiting the server via passing through the NIC? Would having 4GB or more actually improve read/write speeds as this Cached mapping to RAM would be bigger? I'm running v4.5.1 Pro. Thanks.

All unix systems use free memory for caching files and directory structures. If needed this is the first that is going to get freed. This is something good. Yes, it improves performance but not in order of magnitutes (it just depends). And yes, having more memory is always better. unRAID is 32bit but it uses PAE to address more than 4GB memory and use it for instance for filesystem cache.

I might have to give my rig more RAM then . It seems to be fine, it was occupying 1GB out of the 2GB I have, but if I increase it by two fold, more cache RAM could slight improve the performance of my server. RAM is cheap at the moment so I it seems practicable to buy more. Thanks for the tip starcat.

 

All unix systems use free memory for caching files and directory structures. If needed this is the first that is going to get freed. This is something good. Yes, it improves performance but not in order of magnitutes (it just depends). And yes, having more memory is always better. unRAID is 32bit but it uses PAE to address more than 4GB memory and use it for instance for filesystem cache.

Yeap. I also think about putting two more 2GB DIMMs and expanding to 8GB in total.

Really? 8GB RAM? Can you give me statistics or benchmarks on increasing the RAM by four fold would actually be a great benefit, for dollar for value wise? Would it be a great return in performance having heaps of cached RAM? Thanks. 

 

Yeap. I also think about putting two more 2GB DIMMs and expanding to 8GB in total.

I have currently 2x 2GB, will upgrade for better interleaving to 4x 2GB. No measurements, I just see it is full with filesystem cache. I also may run VMware in the near future and more memory will come in handy.

Well let me know what your 'before' and 'after' results from 4GB to 8GB RAM offers you. I don't plan to use VMware Server on it in the foresee future as I already have a VMware ESXi server running my VM's. Thanks. 

8GB of ram will be most useful if you do allot of writes/reads randomly and/or to small files.

It will also help with VMware.

 

When doing rtorrent, the 8GB of ram helped a good deal. But for average file access. it did not help that much.

It does let you keep the directory cache in memory longer.

 

I would say if you have a huge array with many files or the conditions mentioned at the start of this post, then you would see a benefit. Otherwise, it does not really boost unraid's performance in receipt or delivery of files.

Nice to know WeeboTech, actually in some instances when I have to write data to my unraid server, it is kind of like the the old saying 'when it rains it pours', in which I'd write several GB's of data in the one session of having to powered on (from 8 ~ even 100GB at one time), so I could benefit from having 4 to even 8GB RAM then. I'll see what the budget and prices are and see what I can get for my dollars that that point in time. Thanks.