SOLVED Seeking Guidance on Implementing SSD Cache with RAID Z2 for Efficient Data Handling

[bhk]

Hello TrueNAS Community,

I hope this message finds you well. I am reaching out to seek advice and guidance on implementing an SSD cache into a large RAID Z2 pool for optimal data management. My goal is to utilize the SSD as a temporary storage buffer, allowing incoming data to be initially saved on the SSD and later moved to the RAID Z2 pool in the background. This approach aims to efficiently handle incoming data while freeing up space on the SSD for new data.

I am particularly interested in the following aspects:

1. Configuration Settings: What are the recommended settings for configuring the SSD cache with RAID Z2 for optimal performance and reliability?
2. Data Migration: How can I ensure a seamless background migration of data from the SSD cache to the RAID Z2 pool without impacting ongoing operations?
3. Monitoring and Optimization: Are there specific monitoring tools or techniques to track the performance of the SSD cache and make adjustments for optimization?
4. Best Practices: Are there any best practices or lessons learned from the community that I should be aware of when implementing this type of setup?

I appreciate any insights, recommendations, or personal experiences you can share regarding the integration of SSD cache with a large RAID Z2 pool. Your expertise will undoubtedly help me make informed decisions and ensure the efficiency and reliability of my TrueNAS storage solution.

Thank you in advance for your time and assistance.

Best regards,

BHK

 

[jgreco]

allowing incoming data to be initially saved on the SSD and later moved to the RAID Z2 pool in the background.

This is not something that ZFS does, although perhaps you could do it with some external software. You may wish to read one of the many ZFS primers available on the Internet to help you understand the roles of ARC and L2ARC, which are both read caches. These help accelerate the performance of reads, primarily on pools that are already highly stressed with traffic, and can make a pool experiencing such I/O patterns work better. ARC and L2ARC generally don't do that much for you if your pool isn't already very busy, as it is more convenient and less resource-intensive for a pool read request to be fulfilled by the pool if there is no current I/O happening on the pool. ZFS has no SSD write caching of any sort, although it does have the ZIL/SLOG mechanism to help accelerate synchronous write requests.

 

[winnielinnie]

Honestly, I wouldn't feel comfortable trying to "automate" this. You might end up with data loss and unpredictable results.

I have a dedicated "SSD-only" pool that I use as a temporary landing pad for incoming downloads, transfers, and multimedia project files.

Manually, I will move things over to the HDD storage pool, either with File Explorer (over SMB) or directly on the NAS itself (with "cp" or "rsync"). The reason I don't use "mv" is because I'd prefer to consciously delete the files myself, "just in case" the copy operation might have messed up. (And it's just wise to do things slowly anyways.)

The reason I don't do this automatically or with a script is because it's too risky. Simply put. What if there's an error with the script? What if the transfer is interrupted? What if there's an unscheduled reboot? What if the transfer is only partial? What if I am writing new data to the source folder at the same time as one of these automatic transfers? What if I didn't want the files removed from the SSD until later? And so and and so on.

So even though rsync has the option to "delete files from the source after transfer", are you willing to take that risk?

Not to mention the complexity of having different destinations on your HDD pool, which either means more scripts or a more complex script.


EDIT: If it only concerns torrents, then at least qBittorrent has this feature built in. You can instruct it to "Download files here" and upon completion "Move files there".