Use USB 3.0 nvme drive as cache partition

[smic717394]

Hi,

I have a question, I´m in progress of building the nas, so far its working great. I´m using a Supermicro A1SRi-2758F motherboard that have a Atom processor C2758 8 core SOC, 16GB ECC DDR3. I now have 2 drive 2TB as mirror, while I´m experimenting but I will be adding 4 drives WD red 4TB, the OS is installed on a 250 SSD.

I added a Kingston NV1 250GB nvme as a cache drive but the motherboard doesn't have a nvme connector so I added on the usb 3, and so far works great.

The 2 questions, what's the best raid for the 4 drives, and is the 250GB enough as a cache partition or I shouldn't bother with the cache partition?

Thank you.

 

[NugentS]

Don't bother with the cache.
If its L2ARC - you don't have enough memory for that - it will actually slow things down (probably). Also just no. The good news is that it isn't pool critical - so it doesn't really matter when it shits itself
If its SLOG - Just No
If its a special vdev - then remove it as quickly as possible - if you can, which you should be able to.

Its probably L2ARC (hopefully)

As for the new disks - please make sure they are CMR, not SMR
As for what to do with them:

1. Whats your use case?

 

[smic717394]

Hi NugentS,

Thanks for the replay.

The nvme its a L2ARC vdev , just added the other day. Its still in testing so I´m not to worried about, But you say When I add the WD drives I shouldn't add the nvme? What size should I get it this is too small, maybe if its a big improvement or better for the drive I will get a bigger one.

The drives are wd40efax so I think they SMR unfortunately, I should have asked before. Still should be ok, its just as a home nas, backup a couple of computers, plex, nextcloud.

I´ve been using it for a couple of weeks, with the small 2.5" drives and I never seen the cpu jump more than 5%. I´m still looking for a nas case, maybe you can recommend one. I now have it install in a shoebox, the case it the last think I need.

 

[NugentS]

SMR and TrueNAS do not mix. Send em back if you can. If you can't - being brutal, use different NAS software. ZFS and SMR do not mix.
Do not add an L2ARC with the memory/ARC you have. [Certainly not one thats USB attached]
Hmm - 2.5" drives. Are those SMR as well? 2.5" HDD's often are.

As for cases - whatever works for you and what you can get in your location. Given that a NAS tends to run 24*7 make sure you have decent airflow to keep the components cool.

 

[smic717394]

I think they SMR, they just chep wd blue and the other a hgst, extracted from older laptops.

 

[NugentS]

Have you considered unraid or OMV?
Might be a better option given the SMR disks which will work for a while, until something goes wrong

 

[smic717394]

I´ll try to sell the disks and buy CMR if they not recommended. I thought I was close to finish the install... jeje.

 

[jgreco]

16GB ECC DDR3.

Please do not bother adding L2ARC until at a VERY minimum 32GB and probably more like 64GB. At 16GB, you are likely to get bad behaviours and it will likely be slowing you down.

When you add L2ARC, try to size it appropriately. Generally about 5x the size of system memory, so a 250GB SSD when you have 64GB of RAM on the system is probably cool.

 

[smic717394]

Please do not bother adding L2ARC until at a VERY minimum 32GB and probably more like 64GB. At 16GB, you are likely to get bad behaviours and it will likely be slowing you down.

When you add L2ARC, try to size it appropriately. Generally about 5x the size of system memory, so a 250GB SSD when you have 64GB of RAM on the system is probably cool.

Thank you. So If I add 64GB ram i can use the nvme as L2ARC . what you think about the SMR disk I have, should I try to get rid of them while they still new and get CMR ?

 

[NugentS]

Why are you so fixated on using the NCMe as an L2ARC?
Do not use the NVMe in a usb device. If you insist on using it get an NVMe to PCIe adapter and use that. Something like Example Adapter

Also - the first thing to do is run the NAS (with CMR) for a while and take a look at your ARC hit rate. If it >90% then L2ARC really won't help as you are working out of RAM anyway. OTOH if you have a hit rate <90% then L2ARC might help - and then is the time to add it (but make sure you have enough memory / ARC first)

 

[smic717394]

Ok, i removed the nvme, and I´ll forget about. I´ll try to sell the drives and get segate cmr, Its a pity, I paid 450€ thinking I´m buying good drives, but its my fault for not investigating first. luckily I haven even open yet. If I cant sell them maybe I can use them in pairs mirror in 2 pools instead of raid.