SLOG and L2ARC advice

[jjoyceiv]

My planned NAS is coming together fairly well, but I'm still unsure about how I should plan for the ZIL/SLOG and L2ARC storage, if any.

For the SLOG device - I've read conflicting reports, but most say it should be mirrored. I'm looking at a couple of 120gb Samsung SM863 for that job, of which I'd only use a fraction. Should I bother with the mirror?

On L2ARC, this box will have probably 64gb of RAM. If I were buying DDR3 I'd go for 128gb and not think twice, but I'm buying mostly new parts for this box, with only the SSDs and HBAs being used. At this amount of RAM, is it even worth having L2ARC going? If so, is it ill advised to use the remaining space on the SM863s for it?

 

[T_Minus]

Would be good to know what the NAS is used for
And what your pool configurations will be?

If you're not using it for VM datastore and/or not setting sync=always then you may not even need a SLOG device at all.

FWIW I would NEVER use a Samsung SSD for a SLOG though, they have bad latency compared to Intel SSD which makes them a poor choice for a SLOG device not to mention their write performance is < than a S3700 200gb, especially that tiny 120gb, may even be worse than the 100GB s3700.

 

[jjoyceiv]

If I can find a good deal on the likes of an S3700 I'll go for it. Should I get 2x for a mirror? The NAS will be mixed-use - media storage (high-res photos, large PSDs, raw video assets, yet plenty of small stuff as well), backups (Time Machine, something for Windows boxen, and possibly VM snapshots), and the data source for an OwnCloud VM which will be used only to offer up files to outside users from the media storage. It will be replacing Dropbox altogether for internal file sharing, as well as two rather craptacular Seagate 3TB externals being used as the dumps for those photo and video assets. I'll probably keep those externals where they are for a local Time Machine backup too, can't hurt to have another copy.

I'm planning one 8x4tb or 8x5tb RAIDZ2 pool.

It looks like, for maximum data security, I should be setting sync=always (from what I've read). Is that not the case?

Your thoughts on L2ARC?

 

[T_Minus]

There are insane deals right now for S3700 on ebay!
400GB for $160 with Best offer. Way over kill for SLOG but Over Provision that to 10GB and roll with it, and you have a super-fast SLOG. It really doesn't sound like your work load would trigger SYNC if you set it to 'default' though so you'd best set to always if you want to take advantage.

I don't think you need to mirror it, especially for what you're using it for.

With the price of the S3700 400g I'd snag 2 of those, 1 for SLOG 1 for L2ARC. Monitor your L2ARC usage/hit rate and determine if you need it, a bigger one, etc...

You'd be set with that setup and very affordable now days!

 

[jjoyceiv]

With the price of the S3700 400g I'd snag 2 of those, 1 for SLOG 1 for L2ARC. Monitor your L2ARC usage/hit rate and determine if you need it, a bigger one, etc...

Guessing I'm best off OPing the L2ARC drive as well? The full 400gb seems nice to have, but not when it takes up 40gb of RAM I could be using for ARC...

I'll do my best to find those deals. Those *are* sweet... at those prices, I might just use them for my primary VM datastores instead of the PM863s I've been looking at.

 

[T_Minus]

I don't think your intended usage will see much usage/benefit of L2, and SLOG unless you do sync=always.

Maybe spend the $$ on more ram instead.

 

[jjoyceiv]

I don't think your intended usage will see much usage/benefit of L2, and SLOG unless you do sync=always.

Maybe spend the $$ on more ram instead.

Got it, I'll consider it. I'll just grab a cheap SSD for boot for now.