I have been experiencing this behavior for a long time, have read other posts describing similar behavior and finally learned enough to have an idea what might be causing it.

 

First, I am assuming unRAID is using ReiserFS v3. I have not learned enough to know how to check that but have read it is v3.6. If it is not v3 then the rest of what I am going to write is kind of useless.

 

Ok, the problem: When a disk is getting close to full, somewhere above 90%, copying a file to it will often cause an initial pause of 20 seconds or so during which time the light on the data drive flashes continously. Only the data data drive, not the parity drive. Some times Windows will get tired of waiting and time out, resulting in an error. After the initial pause, the copy works fine, unless... There is other activity on the system, for example a preclear. In which case a block of data will be copied after the pause (parity drive light flashes for the actual data copy) followed by another pause, flashing data drive light, of the same duration as the first one. This repeats and repeats until the file is finally copied. A 500m (yes meg) file has taken an hour to copy in this situation.

 

My theory: Based on research and observation I have come to the conclusing that what could very likely be happening is free space bitmap searching. When nothing else is running the bitmap is cached so there is only one pause, however if there is other activity, the cache gets purged resulting in another read of all the bitmaps spread across the partition.

 

My question: Again being a UNIX newb I am wondering if someone can tell me if the patch described by this post is part of the unRAID distribution? It seems to describe exactly what I am experiencing although I never checked the CPU utilization (that newb thing again). Thanks for any feedback.

 

Jerry

 

http://www.mail-archive.com/[email protected]/msg21592.html

Yes, that particular patch has been in the Linux mainstream kernel tree since October 1, 2006 and released as part of Linux Kernel 2.6.19. The Linux Kernel unRAID 4.7 uses is 2.6.32.9 that was tagged on February 23, 2010.

 

http://git.kernel.org/?p=linux/kernel/git/longterm/linux-2.6.32.y.git;a=commitdiff;h=9ea0f9499d15c49df23e7aac4332d830c40e12d0