Reduce available memory to FreeNAS VM?

[RichTJ99]

Hi,

I have a FreeNAS VM (9.10) which has 8x 6TB drives and has it allocated as 22tb of usable space. The VM has 16gb of ram dedicated to it.

Can I reduce the ram to 12gb or is that a bad idea? I realize running FreeNAS on a VM is a bad idea but this is a backup box of my main FreeNAS box. Only usage is nightly rsync from main box to this backup box.

When viewing in reporting / memory.

It shows 2.1gb free, 12.9gb 'wired'.

ZFS shows
Arc Size - 10.7gb
Arc Hit ratio - 67%

Thanks,
Rich

 

[MatthewSteinhoff]

For that use case, you may even be able to get by with less. I'd drop it down to 8G and see if it works.

Cheers,
Matt

 

[RichTJ99]

Hi,

Whats the downside if cutting the ram in half? Will it not boot or will I start losing data?

How do i see if it works vs isnt working correctly?

Thanks,
Rich

EDIT: So according to my sig - I had it at 24gb to start. I moved it from a server that had 64 gb to a server that had 32gb so I changed from 24gb to 16gb in that transfer & it seems to be fine.

Just not sure how to tell if it works or doesnt work after the fact.

 

[RichTJ99]

EDIT: So according to my sig - I had it at 24gb to start. I moved it from a server that had 64 gb to a server that had 32gb so I changed from 24gb to 16gb in that transfer & it seems to be fine.

Just not sure how to tell if it works or doesnt work after the fact.

 

[MatthewSteinhoff]

Whats the downside if cutting the ram in half? Will it not boot or will I start losing data?

The minimum RAM requirement for FreeNAS is 8GB. If you don't see more than a token amount of swap space used, FreeNAS has enough memory so long as it meets your performance needs. I've had FreeNAS boot with just 4GB RAM though I'd never suggest that. Not really sure what happens if you give FreeNAS too little memory. I can't imagine data would be lost. Most likely, file services (NFS/SMB/etc.) wouldn't start. Scrubs might fail for lack of breathing room. Just a guess.

When RAM is reduced, the first casualty is performance. On a write-only (for the most part) system such as your replication target, you really don't care about read performance. If ever you have to restore or use the backup as the primary, you could always throw more RAM at the VM fairly quickly.

Watch your swap. If you're not dipping into fake RAM, you're fine so long as you meet your performance targets.

Cheers,
Matt

 

[RichTJ99]

Hi,

I thought the rule of thumb is 1gb ram for 1 tb of storage. So 22tb = 22gb ram - but 16gb is fine. The swap is totally untouched. 8GB would be great for my needs on the esxi box.

I would hate to have data corrupted by the lower ram though but it doesnt sound like that is an issue.

Thanks,
Rich

 

[MatthewSteinhoff]

I thought the rule of thumb is 1gb ram for 1 tb of storage. So 22tb = 22gb ram - but 16gb is fine.

Thumbs are funny like that.

You have a specific use case: a replication target. You're not sharing any files so you're not eating up RAM with NFS, SMB, AFP, etc. You're pretty close to write-only so you don't need files cached for reading. You don't have any jails, plugins, VMs, etc. You're running FreeNAS pretty much as bare as possible.

Cheers,
Matt

 

[RichTJ99]

Hi,

One last item - I do have SSH, SMART, Rysnc, and SMB services running. I do use the SMB periodically to spot check to ensure Rsync is sending all data.

Sometimes i use the SMB to delete data I no longer need, etc.

It sounds like your saying to try it - i am just trying to figure how i know if its not working correctly but I guess the answer is the reporting should show what sort of resources I am using. Right?

Thanks,
Rich