Changing volume options after creation

[taalas]

Hi,

I recently built a new FreeNAS server and created a Raid-Z2 volume and a dataset. When creating the volume and dataset I used the basic options page (not advanced options), this resulted in a volume which hat lz4 compression enabled and the dedup setting on inherit (from where do volumes inherit this setting)? The dataset inherited both options.

In order to speed up access to the share I disabled both compression and the dedup option on the volume and dataset explicitly. My question: Is this a problem (should I have created a new volume and dataset) or is it fine to change these options? I would prefer not to have to create a new volume and share but wanted to make sure before starting to copy data to the dataset...

 

[dlavigne]

Dedup isn't actually on unless you change it to "on". The default lz4 compression is actually the quickest and most intelligent (e.g. it doesn't try to compress if the file won't benefit from it and compression speed is near real-time).

 

[taalas]

That mean's if I changed the Dedup setting from Inherit to Off on the volume it's technically identical? Question still remains: can I safely change the compression method (or disable it) and dedup on a live volume and dataset or do i need to create new ones? The possibility to change it on-the-fly suggests it's no problem?

 

[cyberjock]

You can change it on the fly. But, any data that already exists will not adopt the new properties. Only new data will have the new properties.

You should read up on dedup before using it though. Choosing to use dedup is extremely demanding on RAM. The thumbrule is 5GB of RAM per TB of data. There also is no upper limit, that's just a recommended place to start. Now if you don't have enough RAM and your system has an unclean shutdown you will be locked out of your pool until you have enough RAM to satisfy the ddt requirements. Nobody will be able to help you if you suddenly need 200GB of RAM to access "the most important data in your life". You either go with the 200GB of RAM or you kiss the data goodbye. Yes, this has happened... too many times.

 

[taalas]

Many thanks for your quick and detailed reply cyberjock!

I didn't plan to use dedup, but I will keep your information in mind if we ever choose to turn it on.

As for compression, I am glad to hear that this can be changed on-the-fly. While I understand that this only applies to data written from the point of the change it is good to know that I can keep my existing volume and dataset.

Thank you for your hard work in these forums!

 

[taalas]

One more question about compression:

I disabled compression on all datasets (and volumes)...the compression ratio is not 1.00x though (having deleted all files, so no compressed files are stored any more). Why is that?

 

[cyberjock]

Not sure. I put in a ticket on that ratio being broken, but it was closed to "not gonna fix"...