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Is this possible (Yet?) - ZFS + SSD Caching


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Background:

 

I currently have a four bay DAS connected to my Thunderbolt dock with a few different HDs in for various things, however I'm becoming increasingly frustrated that I have to be sat at my desk to do Photo Editing. Also I've been trying to do photo editing remotely (slowly admittedly) over VPN which works OK if I point Lightroom at my array (rather than "Master" disk) via NFS.

 

So I now want to add another disk to my UnRAID server, format it ZFS, add an SSD for L2ARC and see how well it will work. Ideally want fast directory indexing and fast performance of recently added/used files.

 

So my questions are:

 

1. Does (or will) UnRAID Support L2 ZFS caching, i.e. L2ARC - I think it does now via Command Line with GUI setup on its way(?)

2. I currently have 32GB of RAM, of which sometimes I'm running a Gaming VM which uses 20GB up. I'm very rarely, if ever, going to be needing fast performance whilst gaming. I assume the ARC will dynamically adjust to whatever free memory there is?

3. I currently have a 1TB SSD via SATA. I was going to replace this with a 2TB M2 (ideally SLC) drive, and make a 500GB volume for L2ARC and the rest as my normal "cache" (Docker, VMs, etc) drive, is this doable?

4. I don't have ECC memory and I don't think fast 3200 64GB ECC UDIMM kits even exist - given this mostly impacts ARC rather than data at rest is this actually a major issue. Given this disk would effectively be "Master" corruption would be annoying...!

5. If I dump 200GB of photos/videos, I assume this will be sent to the memory, then SSD first, then sent across to the HDD. This data would stay on the SSD whilst I edit it (frequently accessed) and then be pushed out when the next set of data is sent across. I.e. The latest data up to a certain size will be cached by the SSD?

6. All the data (after it's been copied from the cache) is on the HDD. So if the SSD fails for example (ignoring data that maybe be a few minutes old and hasn't been flushed to the HDD) would be there. I.e. If I connect the HDD to another machine the data would all be there.

 

 

I think thats all the questions I have for now, some input on what I'm trying to achieve would be interesting!

 

Many Thanks.

 

Edited by Interstellar
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10 minutes ago, Interstellar said:

1. Does (or will) UnRAID Support L2 ZFS caching, i.e. L2ARC - I think it does now via Command Line with GUI setup on its way(?)

For now only manually, see here.

 

11 minutes ago, Interstellar said:

2. I currently have 32GB of RAM, of which sometimes I'm running a Gaming VM which uses 20GB up. I'm very rarely, if ever, going to be needing fast performance whilst gaming. I assume the ARC will dynamically adjust to whatever free memory there is?

By default it will use 1/8 of installed RAM, that can be adjusted, see the release notes, note that with Linux it should not be set > 1/2 installed RAM.

 

 

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On 6/25/2023 at 12:53 PM, JorgeB said:

For now only manually, see here.

 

By default it will use 1/8 of installed RAM, that can be adjusted, see the release notes, note that with Linux it should not be set > 1/2 installed RAM.

 

 

 

 

Great, thanks. Having read through that manual link, it does seem possible for me to create two partitions on my SSD, one 1TB in size (for "normal" cache use, docker, VMs, etc...) and then another 500GB Cache for my L2ARC (Remaining 500GB as unused for wear levelling reasons...), am I right in this?

Secondly, if ZFS doesn't release the memory once pressure ramps up, I might make this 2GB initially. Then if/when I get 48/64GB of ram I might crank it up to say 8GB's worth. TBC!

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Can I do this a different way then, can I split my 2TB into 1TB for array cache (or anything that I can put VMs/Docker on) and then 1TB to be pass through’d for gaming VM instead of a PCI-E pass through?

 

E.g.

 

/dev/sda1 - Cache for VMs/Docker

/dev/sda2 - Block device for primary gaming VM?

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