Freenas ISCSI target. 4GB memory only

[silver565]

Hi Everyone,

I'm looking at building a small freenas box that will run two 120GB SSDs as an ISCSI target for two ESXi hosts.
Basically, I will add this new setup to my study lab for ESXi. I want to map two 120GB SSDs as ISCSI targets to two hosts.

Will a small system with 4GB of memory be enough?

 

[anodos]

Hi Everyone,

I'm looking at building a small freenas box that will run two 120GB SSDs as an ISCSI target for two ESXi hosts.
Basically, I will add this new setup to my study lab for ESXi. I want to map two 120GB SSDs as ISCSI targets to two hosts.

Will a small system with 4GB of memory be enough?

Read the hardware stickies and freenas handbook. 8GB ECC.

 

[Ericloewe]

Well, that's a silly question, given that everything says 8GB is the minimum amount of RAM...

 

[L]

I would test it. The RAM requirements are based on HDD. This is really a small quantity of disk and being ssd, the cache flushing should be quite rapid and the way memory is managed should be much more efficient. Everything changes with ssd. Things like not recommending dedup starts to change. I would test it. Let us know what you see. This is less than a TB of disk space. Check your ram usage by running vmstat in a shell.

 

[cyberjock]

I would test it. The RAM requirements are based on HDD.

No, they aren't.

 

[L]

So how were they calculated??

I have run the math many times and can't figure out where 8GB comes from? Native freebsd takes about .5 GB, the gui, run at about .5GB, calculated all the zfs caches, about .1GB, I would add a apx 1GB for each very active 1gbe, nfsd and smbd run a little fat and probably .5GB per client. afp about .3 On my system running 1 of each client on 1gbe, i run at about 2-3GB usage. I haven't calculated the iscsi, but will with the inkernel.

 

[jgreco]

8GB comes from the fact that we kept running into panicks and pool losses with less. There is no math involved, just good old sysadmin-class observation and remediation. I made an observation based on lots of reports in the forums and bumped the minimum from 6 to 8. I note that we haven't seen pool loss on 8GB even with massively larger-than-8TB pools though of course performance suffers horribly. There's likely a pool size, maybe out past 40TB, where 8GB would cease to be sufficient, but no one seems intent on trying this so I'm not worried about it. Since the goal of a required minimum is that the appliance not catastrophically malfunction, and 8GB seems to be that threshold, that is what it is set at.

 

[jgreco]

Oh. I did mean to add that typically VM uses are very stressy and that you probably want to set a 16GB minimum. It ought to work with 8 but performance could be very dodgy especially as you fill the pool. SSDs are NOT magic despite what some people say.

 

[L]

I would want to put less in ram with an all ssd. I would probably like to see primarycache=meta

I see the vote for this... I don't know. I would need to test your exact setup.

 

[cyberjock]

What jgreco said. I tried to explain the 8GB of RAM minimum to you on the phone, and I am pretty sure you've been called out at least 3 times on the 8GB of RAM *minimum*. It doesn't matter if you like it, it doesn't matter if you don't understand it (we don't even understand it for 100% certainty). But good ol' observation tells us 8GB of RAM is the minimum for a stable system. Take it or leave it. Those that disagree are welcome to disagree, but the community will quickly label you as uninformed and not trustworthy if you can't accept the overwhelming evidence from before.

 

[jgreco]

Some of us already have done so.

Testing setups with less than 8GB is not proof that such will be stable and reliable; at best you will get away with it but if it burns you then .... (Nelson Muntz) Ha, ha! Hope it was worth it.

It is 2014 and 8GB is no longer an onerous amount of RAM.