Comments on: The ZFS ZIL and SLOG Demystified

By: Joon Lee

Joon Lee — Fri, 08 May 2020 23:14:40 +0000

In reply to Joshua.

Joshua, check out this thread: https://www.ixsystems.com/community/threads/ssd-for-caching-question.49060/
Also, how much RAM is in your system?

By: Joshua

Joshua — Fri, 01 May 2020 20:26:59 +0000

Cache drives will they benefit a Video Editor in a FreeNAS build or not? Its for storing my films, and audio clips

By: Eric Murach Jr

Eric Murach Jr — Thu, 05 Dec 2019 01:16:07 +0000

Ok sync vs async. So Sync for SLOG. Async nomally not? But what in case Sync=Always. I’m slower now if thats that turned on right?
I read a write-up. It touch on that SMB doesn’t have sync. So, does that mean if all your shares are Windows SMB, It always doing Async xfrs and never sync transfers? If so if Sync=Standard does that mean the in that case the SLOG is never used? But, what if you set the the Sync=always would that force it to be used in that case? I’m just running a home NAS setup for media files mostly. A big setup yes. But not doing VM and no NFS shares as yet. I what the data protection yes but does that mean I need to set Sync=always so it would use the SLOG and provide the faster slog with the lease latency. If got Base 10-T lan and SAS3.

By: audi6

audi6 — Mon, 05 Aug 2019 12:45:28 +0000

“You can mirror your SLOG devices as an additional precaution”
I already had SSDs that have been failing silently. Result was a corrupted file system, probably because data got corrupted during SSD writes. Assuming that this will happen to my SLOG, will a mirrored SLOG help here?

By: Lee E

Lee E — Thu, 02 May 2019 14:06:06 +0000

My critique:
Says – “What is not obvious however is that they only come into play under very specific circumstances.”
Then proceeds to not actually explain what those very specific circumstances actually are, just that they obviously happen during async, which is most of the time by default. We even end saying that all Truenas systems come with a SLOG, which really seems to ultimately contradict the initial impression that SLOG would only be used in certain configurations and instead lead us to believe it should always be configured if SSD storage can be made available for it.

By: Truman HW

Truman HW — Tue, 08 Jan 2019 05:28:14 +0000

1. Thank you … but. (No, really — thank you).
Why not differentiate ZIL, SLOG, L2ARC ….
explain which are synonyms or how they’re different
example-tasks that rely on each term …
devices with substantial vs. inconsequential performance differences.
how to know if the SSD / Cache-device is failing
what those consequences are.
🙂
Where optimal CPU cost-benefit is…
WHY the shape of transfers in the network monitor is a quarter of a circle.
??? SO CRAZY! What IS that? 😀 THANK YOU!

By: Richard Elling

Richard Elling — Mon, 08 Oct 2018 21:12:46 +0000

It is not really accurate to lump NFS into the always-sync camp. Starting with NFSv3, there is an async write mode. And, unsurprisingly, async write + commit, works mostly like ZFS with the difference being the scope of the commit.

By: Joon Lee

Joon Lee — Sat, 15 Sep 2018 00:24:32 +0000

In reply to Ulf. Yes, you really do need 2 SSDs.

By: Ulf

Ulf — Mon, 20 Aug 2018 22:35:17 +0000

Can the boot SSD also be the SLOG drive at the same time or do I really need to add 2 SSDs?

By: Joon Lee

Joon Lee — Wed, 28 Jun 2017 19:34:06 +0000

In reply to wayne. Depends on the hardware and usage whether or not it will benefit from slog, best to make a forum post describing setup!

By: wayne

wayne — Thu, 15 Jun 2017 01:04:45 +0000

just want to be clear in my understanding, I can mirror SLOG SSD of say 64Gbps each, and this should be sufficient for both i/o performance increase, as well as protection of system failure in middle of a write?

By: Mike

Mike — Tue, 09 May 2017 15:29:03 +0000

In reply to Brian. This is something you should never attempt outside of just for fun. This will destroy your drive in under a week. Not to mention this is a non supported configuration.

By: Joshms

Joshms — Thu, 30 Mar 2017 23:01:20 +0000

In reply to Brian. I'd highly recommend checking out our forums! There are a lot of people that may be able to pitch in and help answer your question.

By: Brian

Brian — Fri, 10 Feb 2017 16:51:37 +0000

Thank you for the excellent write up. I am a new to ZFS as of recent and have begun my own setup. I have 8 sata drives setup as my main pool and 2 SSD’s 1 set for my Freenas OS (9.10)and another set to an L2ARC. When I setup the L2ARC I was attempting to divide the drive for a portion allocated to L2ARC and another to ZIL but could not find a means to do so. I assumed it was restricted similar to how the OS installed (forced to take the entire drive). Short of adding a 3rd SSD is there a means to use both an L2ARC and ZIL on just one of my SSD’s together?

By: Greg P

Greg P — Sun, 27 Dec 2015 21:50:16 +0000

Just leaving a comment to show appreciation for Michael taking the time to write this article. Even though I am a long-time user of FreeNAS with many running systems, I always seem to learn something from these pieces. Regularly check for new articles and am excited to see each new one even though I think I have a real life.

By: Ashley Choo Tim

Ashley Choo Tim — Fri, 13 Nov 2015 10:51:45 +0000

I really appreciate these articles from the FreeNAS Newsletter. It’s easier to learn about the technology with the short but informative pieces. Thank you Michael for this!