L2 Arc Issue?

[kspare]

I have a 1.2tb L2 Arc and it's doing something weird. it's stuck at 400gb right now.

It used to sit around 1Tb.... I'm running FreeNAS-9.10-STABLE-201605021851 (35c85f7)

Any ideas?

 

[Mlovelace]

You should file a bug report.

 

[m0nkey_]

You don't need a L2ARC device. You have 64GB RAM and a pool size of 48GB, so you're above the 1GB:1TB rule of thumb. Your system will likely perform better without it.

 

[DrKK]

You don't need a L2ARC device. You have 64GB RAM and a pool size of 48GB, so you're above the 1GB:1TB rule of thumb. Your system will likely perform better without it.

Yeah, I want to amplify this. Your L2ARC is probably not in use at all, really. Also, you have a 1.2TB L2ARC? Sir, that does not sound like a proper L2ARC, since L2ARC will normally be very high speed SSDs.

Bottom line: if you have 48TB pool, and 64GB of RAM, it would be unlikely that your L2ARC is actually serving any hits, and it is 99.9% sure that whatever it's doing, it's not improving your performance. In fact, there are technical reasons to believe that in this configuration, the L2ARC is making your system *SLOWER*.

I don't think your L2ARC is misbehaving. And, as I said, in any case, I think you may be best advised to not use an L2ARC. You'll find several bits in the forum and in the documentation which should convince you that it would be a very, very strange workload that would require an L2ARC in your situation.

 

[DrKK]

You should file a bug report.

I don't agree. It's not a bug. It's what happens when an L2ARC is foundering/pointless.

 

[Mlovelace]

Well the arc usage says 231G max so I'm guessing it's not the system in the signature.

 

[DrKK]

Well the arc usage says 231G max so I'm guessing it's not the system in the signature.

Well I was going by what @m0nkey_ said.

 

[Mlovelace]

Well I was going by what @m0nkey_ said.

I just looked at what kspare posted and that the normal behavior of his system has changed for the worse. Hence the bug report suggestion, if it's not a bug no harm no foul, but why not check it out.

 

[jgreco]

Yeah, I want to amplify this. Your L2ARC is probably not in use at all, really. Also, you have a 1.2TB L2ARC? Sir, that does not sound like a proper L2ARC, since L2ARC will normally be very high speed SSDs.

Actually I'm pretty sure he's using an Intel 750 or maybe one of the DC SSD's. There's no reason to think that there's a problem with that. Since the L2ARC used to be stable around 1TB (~expected behaviour IMO) and is now waffling, that's potentially an issue. Someone with some knowledge of what's changed in the latest updates might have more insight into this; to me, it just looks broken somehow.

 

[Mlovelace]

I guess I need to up my post count so people believe me ;)

 

[jgreco]

I guess I need to up my post count so people believe me ;)

Upping your post count doesn't actually make people believe you, trust me.

 

[DrKK]

Upping your post count doesn't actually make people believe you, trust me.

He speaks from experience.

 

[Mlovelace]

He speaks from experience.

Yeah, I was just joking about it. @kspare You could try rolling back the update that broke your l2arc while you wait for the bug report to be looked at.

 

[anodos]

Upping your post count doesn't actually make people believe you, trust me.

If you want people to believe you, just tell them what they want to hear. "Yes, smothering your NAS with a pillow is a great idea."

 

[Sakuru]

The L2ARC on my WorkTEST box waffles too. I just assume it's garbage collection or something. It's running 9.10-STABLE-201604111739

 

[cyberjock]

L2ARC stuff *can* be evicted if ZFS decides its of no value. Then, if there is no data worth adding to the L2ARC, the size will shrink.

This sounds totally normal and is nothing more than fluctuations in the usage of the system. Of course, a chart isn't really good enough evidence to argue that a bug doesn't exist, but it doesn't confirm all is "okay" either.

 

[kspare]

Hey guys, sorry I forgot I posted this.

I did a mass move on the box and it topped out. I think its just what cyperjck said above. We aren't pushing the box hard enough to make it go larger.

I just moved a large amount of data on that box as I burn in some drives on my other san.....got a bad 4TB RE drive. so decided to do a burn in on the whole pool.

For laughs I did it on a 400gb Intel 750...it's got decent speed lol.

Anyway my l2arc goes up depending on what im doing.