Recommended ZFS compression level for an Intel Atom 2500 with 4GB of ram

[rick6]

What would be the recommended ZFS compression level for an Intel Atom 2500 (1.8ghz) with 4GB of ram? When opening "Edit ZFS Options" i get various options for compression level but since this isn't the more powerfull cpu and 4GB is just barely ok for zfs i have my doubts which to pick since i would like to get the most of my hard drives space as possible.

Also there is a setting right bellow the compression config saying "Enable atime" with the options "Inherit", "On" and Off". What does this do?

Many thanks in advance!

 

[Stephens]

http://www.lmgtfy.com/?q=freenas+atime

 

[ProtoSD]

http://www.lmgtfy.com/?q=freenas+atime

LOL!
Stephens that made my day! Didn't know about lmgtfy.com ;) I'll be sure to use that myself.

 

[rick6]

http://www.lmgtfy.com/?q=freenas+atime

I did two questions in my post, being the first the main topic of the thread and the second a minor one but also important. Google it? Not a bad ideia but if i asked here is because i wanted your quality explanation about that, the same quality explanation i know the users of this forum are able to give for their knowledge and experiencie... and who knows if one could even get some tip coming from personal experience that you wouldn't usually find in a simple google search.

I actually use to do my searches, this time i didn't (about the second question, i did google the first). In a forum which the purpose is to awnser questions made by noobs on the subject like me, hints like "google it" sort of awnsers are in a way rude.

Thanks for the help though.

 

[rick6]

So, back to my initial question. Using compression on a Atom is something to be careful with because of low performance with high levels, but is it normal if i use the maximum gzip level (9 i suppose) for the system to hang completly making me needing to reboot ?

I find it odd that the cpu usage wont go high while doing it so. It raises up to 25%\46%, i would expect more for an Intel Atom.

I'm seeing it here http://doc.freenas.org/index.php/Display_System_Processes so i'm not sure if there would be a better way to check the cpu usage besides the "Display System Processes" window.

For now i'm using lzjb compression as it seems to be the fastest and stable.

 

[cyberjock]

...but is it normal if i use the maximum gzip level (9 i suppose) for the system to hang completly making me needing to reboot ?

I LOL'd when I saw that comment. Heck yeah. Compression is CPU intensive. Some more than others. I'd fully expect you to be very disappointed with performance if you use gzip.

Honestly, I'm surprised you are happy with any compression. Atom's aren't power houses, but they are very energy efficient. I wouldn't have built a server with an Atom CPU if I intended to use ZFS compression.

 

[rick6]

Haha, well yes i'm happy with it. Although i wasn't aware of how hard this type of compression would be on the cpu because i'm still pretty newby on the subject, i'm not as worried with performance as much as i am with having all backups done while using the hdds space as best as i can! I'm able to get between 20\50mb\s when transferring data. When i do backups i don't care much that it takes time and as long as i am able to stream 1080p videos i'm ok with it.

All-in-all, lzjb seems to be the best so far for this cpu. Actually and oddly enough, it seems to transfer faster than if no compression at all was enabled. Maybe because the cpu is able to compress fast enough and therefore there's not so much data to write on the harddrive.