Hi,

 

I just got a storage server up and running using some pretty old hardware.

It basically all works nicely and I get decent enough transfer speeds via Gigabit Ethernet (55MB/sec on average).

 

But...

 

The original motherboard was equipped with only 512MB of DDR RAM (PC3200). Since I read that would be the very minimum I went ahead and bought 2GB of RAM (2x1GB) to replace it.

 

 

As soon as I run the server with the full 2GB of RAM those stable 55MB/sec get very unstable. Monitoring the ethernet traffic I could see that the network transfer speed drops to 0Bit/sec several times a minute.

 

After eliminating network issues or the source of the transfer as the cause (using different targets and sources and different network equipment) I can definitely say that the problem is caused by the unRAID server having more memory.

 

If I use just 1GB of memory the transfer speeds are still unstable but they don't drop all the down to 0Bit/sec but just down to something like 100MBit/sec.

 

I was able to reproduce the behaviour several times both with single multi GB files and multiple <1GB files.

 

Monitoring the activity on the unRAID server with top just showed that kswap and flush got active repeatedly. I assume the system is using the 2GB RAM as cache and then has to flush it to the HDD every once in a while. Apparently this process is not working properly.

 

Should I not equip an unRAID 5 server with 2GB of RAM?

Or is there a way to configure/tune the RAM caching behaviour to get rid of this problem.

 

Thanks a lot & best regards,

Marcel

Unraid 5 handles upto 4gb of ram natively, and can support more than that despite it being 32bit only through PAE. The trouble with unraid5/32bit is how the ram is divoded i to 2 sections, lower ram and upperram. It is enitrely possible to run out of lower ram while having tons of upper ram available.

 

Also, unraid5/32bit required quite a bit of fine tuning to get running smoothly.

In terms of tuning...

 

I have adjusted the values for md_num_stripes, md_write_limit, md_sync_window as suggested on the LimeTech website for systems with >1GB RAM (2048, 768 1024). Unfortunately without any improvement.