Local storage vs. NAS and L2ARC SSD

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Local storage vs. NAS and L2ARC SSD

Post by akindo » Sun Nov 11, 2012 10:10 am

Hi all

I've just bought a Mac Mini 2012 model with a 1TB SATA-600 5400 RPM disk and 16GB RAM. I already run a NAS with 3 x 2TB SATA-300 5400 RPM disks in RAIDZ and Gigabit Ethernet.

A prime function of my machine will be image editing of RAW files which are 25 - 50 MB in size. I'll also do some video editing.

I am thinking to buy an SSD to install OS X on and then run Zevo on the 1TB disk.

I have some questions regarding local disk performance vs. what I can get from the NAS and regarding L2ARC caches:

1. From the mechanical disks I'll get about 125 MB/s out of them, so just about hitting the GigE barrier. How much better performance will I get by storing my entire image library on the 1TB disk which is connected via SATA-600 or USB 3 compared to storing it on the NAS? I can see that I'm dealing with the following transfer rates: SATA-600: 600 MB/s, USB 3: 500 MB/s, Gigabit Ethernet 125 MB/s. It seems to me that GigE won't be a barrier but when I've tried to attach one of the 2TB disks from the array to the local computer, it just seems snappier.

2. Would it be wise to buy two SSDs instead of one (one for OS X and one for a L2ARC cache)? I'd then attach the 1TB disk via USB 3. The other option would be to manually copy over working projects of images from the 1TB drive/NAS to the SSD, edit them, then move them back. The Mini will be on for months at a time (but in standby at night). Will the L2ARC help in my typical workload?

Thanks for any help! :ugeek:
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link

Post by grahamperrin » Sun Nov 11, 2012 10:53 am

Around a month ago in the FreeNAS area I bookmarked
ZFS and SSD cache size (log (zil) and L2ARC) (2012-03-12)

I'm not a user of NAS but the discussion looks good, and I guess that many of its points are applicable to a user of OS X. In particular:

TScott wrote:… from what I've read your money is always best spent on memory (ARC) before an SSD for L2ARC (as memory is noteably faster). Along with that, its vital not to oversize your L2ARC, because system memory (ARC) is used by ZFS to manage L2ARC. The larger the L2ARC pool, the more of the main, much faster, system memory is eaten. …


So I guess, consider the memory constraint (of the Mac Mini) before investing too much in an L2ARC-oriented SSD.
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Re: Local storage vs. NAS and L2ARC SSD

Post by akindo » Mon Nov 12, 2012 2:16 pm

Hi Graham

Thanks for your answer. :) I'd just stumbled upon that thread yesterday as well. Good point about the memory. My Mac Mini is maxed out with 16 GB RAM, but I wouldn't want too much to get eaten by ZFS due to a large L2ARC. In the end I ordered a 256 GB SSD which will house OS X and the projects I'll be working on in the short term, then I'll move them back when done. Thought about getting a smaller SSD for my server as an L2ARC, but it can't have more than 4 GB RAM so maybe this isn't such a good idea in the end. I'll just leave it for now.
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Re: Local storage vs. NAS and L2ARC SSD

Post by grahamperrin » Mon Nov 12, 2012 8:18 pm

akindo wrote:… smaller SSD for my server as an L2ARC, but it can't have more than 4 GB RAM …


If that server has more than one hard disk with a JHFS+ slice, and if a smaller SSD is already on the shopping list: consider moving a journal (but not of the startup volume) to an Apple_Journal slice of the SSD.
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