Question: There are several posts pointing to the fact that a full disk (reiserfs specific or not) will cause performance issues in writing (and possibly reading).

 

I can however find nowhere what would be a possible (And approximate) treshold for this. Should I keep 2% free, 5%, 10% or even more ?

 

And is this slowdown only expected when writing ?  For my disks containing movies that would be no issue since they are basically only written to once..

In my experience, when the filesystem starts getting full or you have many many files, resierfs has delays when starting to write new files.

 

I would say around 85%/90%.

This is exasperated as the drive fills and you are using the slower RPM drives with smaller cache.

 

In my situation, I would move a file to a drive that was close to full, I would see all this activity on the drive without any data being transferred. Sometimes this would take minutes. Sometimes it would be so long that the Windows/Samba connection would time out and the copy would fail. Usually a retry was successful since some of the filesystem data must have been cached.  For me dir_cache script did not help, nor did a find down the whole tree before the copy.

 

Once the write had started, the speed was relative to the drive's speed and how full it was. I rarely experienced less then 11MB/s.

 

Okay... so 80% should be safe for drives that are write intensive... I should be good then... I have a lot of drives that are 95% full but they are sitting there waiting till a movie is needed, there is no writing going on..

I can't say it's safe, because I had drives that were not as full, but had many files.

A write would cause a search down all the inodes for the directories and what I suppose is a free block.

If you have large movie files, you can fill the drive up, leaving some room for house keeping. i.e. 2-3%.

The only issue will be the filling speed will diminish as the drive gets nearly full.

 

For write intensive drives, I would keep them as free as possible.

Use the fastest drives with the largest cache.

 

I.E. my /home, download, source and other write intensive folders are on the fastest drive I have (i.e. until I upgrade).

There is measurable difference in seeking for new blocks on a 5400 RPM drive vs a 7200 RPM drive as the drive capacity gets used up.