Should I really keep the occupied space below 80%?

[sebkar]

Hi

I recently filled my FreeNAS up to 80% and got a warning that is should be below that. I did some quick googling to find out why and found a Reddit thread that basically said that it's from "back in the days" and not really important anymore. What will happen however is that the performance will get worse if you go past 95 % (or something similar). But there's never really any risk to lose data as long as you have a bunch of free GB.

Can't find the thread anymore but I remember that there were others who agreed with the user. But I thought I would check with you guys first. Is it safe to fill my drives to, lets say, 95%?

 

[danb35]

Is it safe to fill my drives to, lets say, 95 %?

Safe? Probably. A good idea? No.

 

[Ericloewe]

It is not a particularly good idea.

Exceeding 80% by a bit is not the end of the world. It is, however, the point where you should go "how did it come to this?" and arrange for some more free space.

95% is the "oh crap" point you must avoid if you don't want a bad day.

 

[sebkar]

Safe? Probably. A good idea? No.

Why wouldn't it be a good idea if you consider it safe? And where would you say it gets bad, 80%, 90%?

Exceeding 80% by a bit is not the end of the world. It is, however, the point where you should go "how did it come to this?" and arrange for some more free space.

I use it mainly as a media server so the space get cramped pretty easy. I cleaned it up a bit so it should be fine for maybe another year though, but eventually I will fill the drives. And unless the prices go down it will be expensive upgrading the drives.

 

[Ericloewe]

Why wouldn't it be a good idea if you consider it safe? And where would you say it gets bad, 80%, 90%?

1. Things get increasingly slower.
2. You've broken down the mental barrier keeping you reasonably far away from the nastier situations.
3. You really, really, really, really don't want to fill up your pool.
4. If ZFS switches to the space-efficient allocator, performance takes a nose dive.
5. Everything grows, for a number of reasons. It's not reasonable to assume you can safely keep a large volume of data close but not over the edge for a significant amount of time.

 

[wblock]

You've broken down the mental barrier keeping you reasonably far away from the nastier situations.

That is a good point. Some of us have that barrier at 50%, because it becomes impossible to make a second copy of what is already present on the disks.

This whole question is kind of like asking "How fast can I drive on this icy mountain road with steep curves and sharp turns?"