FreeNAS what SSD to choose for caching

[mst]

I wonder how big and what model should be for caching. ..... Thank you

 

[MatthewSteinhoff]

That's a complicated question and you've provided no information about your existing hardware or FreeNAS use case. Thus, unanswerable in any intelligent fashion.

But that's not going to stop me: you probably don't need L2ARC. If anything, you need more RAM.

Provide more details and I'll be happy to give you a more informed answer. (Though, if you want to save yourself the time and effort, the answer is probably still going to be more RAM and skip the L2ARC.)

Cheers,
Matt

 

[mst]

Thank you Matthew,

The reason is I have found this link
https://forums.freenas.org/index.php?threads/ssd-for-caching-question.49060/

I have Supermicro Chassis with 32GB of RAM and 12 TB 7200RPM +14 3TB 7200 RPM drives, I was wondering if giving one 120GB of SSD would boost up performance a bit. In my case I use it with VCENTER over ISCSI dedicated 10GB network. Thank You,

 

[melloa]

If anything, you need more RAM.

You know, @MatthewSteinhoff , I have to agree with you from my ZFS-nOOb perspective.

Just add memory to my box and the transfer speed tripled on a large file.

 

[Chris Moore]

Thus, unanswerable in any intelligent fashion.

But that's not going to stop me:

Great answer

I have Supermicro Chassis with 32GB of RAM and 12 TB 7200RPM +14 3TB 7200 RPM drives, I was wondering if giving one 120GB of SSD would boost up performance a bit. In my case I use it with VCENTER over ISCSI dedicated 10GB network.

You still are not giving enough information about your system to be useful. Maybe if you review the forum rules, you would understand better what it is we are looking to know: https://forums.freenas.org/index.php?threads/updated-forum-rules-4-11-17.45124/

The first thing to improve in any FreeNAS system is the amount of RAM because the system uses RAM for the ARC (Adaptive Replacement Cache) and that helps to accelerate the functionality of the system. You might be able to improve your performance on synchronous writes by adding a very fast NVMe SSD, but a SATA SSD is most likely going to be overwhelmed and unable to provide any significant boost to performance.
Review these threads to see some data on the subject:

Slideshow explaining VDev, zpool, ZIL and L2ARC
https://forums.freenas.org/index.ph...ning-vdev-zpool-zil-and-l2arc-for-noobs.7775/

Terminology and Abbreviations Primer
https://forums.freenas.org/index.php?threads/terminology-and-abbreviations-primer.28174/

The ZFS ZIL and SLOG Demystified
http://www.freenas.org/blog/zfs-zil-and-slog-demystified/

Testing the benefits of SLOG
https://forums.freenas.org/index.php?threads/testing-the-benefits-of-slog-using-a-ram-disk.56561

 

[MatthewSteinhoff]

32GB of RAM and 12 TB 7200RPM +14 3TB 7200 RPM drives, I was wondering if giving one 120GB of SSD would boost up performance a bit. In my case I use it with VCENTER over ISCSI dedicated 10GB network.

I'm still unclear how much active storage space you have. Assuming (12 x 1TB @ RAIDZ2) + (14 x 3TB @ RAIDZ2), you've got 46TB of storage? The rule of thumb is a gig of RAM per TB of storage. With just 32G, you're already short on RAM. Will your motherboard support more RAM?

What is your current ARC size and ARC hit ratio?

What sorts of performance problems are you seeing? Are reads slow or are writes slow? What is your actual pool layout - RAIDZ2 or striped mirrors?

An SSD SLOG may of more help than an SSD L2ARC.

Cheers,
Matt

 

[Chris Moore]

PS. also these links:

SLOG benchmarking and finding the best SLOG
https://forums.freenas.org/index.ph...-and-finding-the-best-slog.63521/#post-454773

Testing the benefits of SLOG using a RAM disk!
https://forums.freenas.org/index.ph...s-of-slog-using-a-ram-disk.56561/#post-396630

 

[kdragon75]

(L2ARC size in kilobytes) / (typical recordsize -- or volblocksize -- in kilobytes) * 70 bytes = ARC header size in RAM.
~500,000,000 / 4096 * 70 = 8,544,921.875
In your case that's about 8GB of RAM that is NOT used in the ARC. If your running less than 50 home lab VMs, I'm willing to bet your getting LESS performance. That's if you system is not crashing due to running out of memory!