SOLVED Possible to replace failed ZIL with a smaller drive?

[hexadecagram]

Subject says it all.

I need to replace the ZIL in an encrypted (GELI) pool. All I have on-hand are smaller SSDs. As I understand it, ZIL drives do not need to be big at all, so I would think this should not matter.

However, the FreeNAS UI says "device is too small". And if I try again it complains that there are now ZFS labels on the disk.

I would really rather not have to buy a new SSD if possible. Can I salvage this?

 

[Chris Moore]

The ZIL and SLOG are two different (although related) things. When you are using a SSD as you describe, you have moved the ZIL, which is stored in the pool to a Separate LOG device (SLOG) and the description SLOG should be used to describe the situation as the ZIL, which is inside the storage pool, can never be removed. You can remove the SLOG device completely from the pool and the pool can survive that process. Then you can add a new, smaller, SLOG device to the pool. You can not replace directly a larger device with a smaller device.

You may find a better discussion of the subject, but I think this is a good starter for your reading:

safely remove slog

Hi, I am a long time reader first time poster. I made a BIG mistake on a FreeNAS setup. I used a USB flash drive for the (zil/slog) and now I need to remove it. I followed this post to set it up in the terminal instead of using the web gui...

www.ixsystems.com

 

[hexadecagram]

Thank you for clarifying that! It has been some source of confusion for me for a while now. Does that mean that the L2ARC would be housed by a device called the SCACHE?

I was able to remove the old SLOG from my pool and then extend the pool to include the new drive as SLOG through the Web UI. I seem to recall having to encryption re-key in order to get it be unlocked on boot.

 

[Chris Moore]

Thank you for clarifying that! It has been some source of confusion for me for a while now. Does that mean that the L2ARC would be housed by a device called the SCACHE?

No. ARC (Adaptive Replacement Cache) is in RAM. L2ARC is the Level 2 Cache that allows the system to have more cache without needing massive quantities of RAM. L2ARC is typically done with SSD, but I have also seen it done on a large quantity of fast spinning disks when 15k RPM disks were the "in thing" for high performance disk and SSD was prohibitively expensive.

Here is an article that talks about it in greater detail. Even though the article was published in 2010, the concepts have changed very little:

Explanation of ARC and L2ARC » ZFS Build

 

[hexadecagram]

Thanks very much for the help, Chris! I'm marking this thread as solved.