So... what will happen on systems that are ram limited

[timvanhelsdingen]

So i'm building a freenas server soon and i'm planning to put in a reasonable amount of ram (64gb for the 64tb that will be in it) but that will obviously not be enough if i ever decide to grow the pool.
So, I'm just wondering, what exactly happens if you don't have enough RAM? Yes, I know performance suffers. But in what way? If all it means that it falls back to pulling stuff from disk then that doesn't sound too bad in my opinion (i'll be striping so won't be too bad). Or will the pulling data from disk also suffer?...
Can't really find anything on how lack of ram impacts the server apart from it having to pull more from disk (which I don't mind too much, as that's already happening in my current non-ZFS setup)

 

[garm]

64gb for the 64tb that will be in it

You’ll be fine

i'll be striping so won't be too bad

Don’t do that, that will not provide any healing capability and you will eventually lose the pool

 

[timvanhelsdingen]

You’ll be fine

Don’t do that, that will not provide any healing capability and you will eventually lose the pool

It's mirrored striped, so should be fine :)
But could you explain what happens if you don't have enough ram? Let's say if i'd later add extra 64tb (for 128 total), which kind of issues would it give if i'm still on the 64gb of ram/

 

[Chris Moore]

It's mirrored striped, so should be fine

You should look at some of these resources to help you with your terminology and reduce misunderstandings.

The 'Hidden' Cost of Using ZFS for Your Home NAS
https://louwrentius.com/the-hidden-cost-of-using-zfs-for-your-home-nas.html

Slideshow explaining VDev, zpool, ZIL and L2ARC
https://www.ixsystems.com/community...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

Overview of ZFS Pools in FreeNAS from the iXsystems blog:
https://www.ixsystems.com/blog/zfs-pools-in-freenas/

Terminology and Abbreviations Primer
https://www.ixsystems.com/community/threads/terminology-and-abbreviations-primer.28174/

Why not to use RAID-5 or RAIDz1
https://www.zdnet.com/article/why-raid-5-stops-working-in-2009/

 

[Chris Moore]

The requirement for "enough" RAM is covered. You have 64GB. You can run into reliability problems if you have less than 8GB. More memory than you have already stipulated to may improve your performance, depending on exactly what you plan to use the system for.

 

[timvanhelsdingen]

The requirement for "enough" RAM is covered. You have 64GB. You can run into reliability problems if you have less than 8GB. More memory than you have already stipulated to may improve your performance, depending on exactly what you plan to use the system for.

Thanks for the reply.

I am aware on the different pool types and i need striped/mirrored vdevs as NAS is aimed for performance, not specifically having more storage.

I've read up on most of those lot resources already regarding the recommendations. I know it's on spec currently with what's recommended, i however can't find any resources on the exact performance drops of not running in spec (like only running 0.5gb per Tb) that's why I made this post as I'd like to know how much of a drop I could expect and if it could dall below the striped speed of the 4 drives for example, or if will just not be any faster than that as nothing is coming from cache.
My main concern wanting to expand the drives later to 128gb and then falling to super low transfer speeds because it's not the 1gb per Tb recommend. Can't find any benchmarks on this anywhere which use striped/mirrored vdevs.

 

[Chris Moore]

Can't find any benchmarks on this anywhere which use striped/mirrored vdevs

Not the correct terminology. All vdevs in a ZFS pool are always striped with each other. Description of a pool is done at the vdev level because all vdevs should always be equal to each other. Normally a pool is described as (for example) RAIDz2 or mirrored. The number of vdevs will impact performance. I have benchmarked my iSCSI pool (8 mirror vdevs) and posted that in the forum. You could probably find it with a search.