Benchmark/check L2ARC performances

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Re: Benchmark/check L2ARC performances

Post by grahamperrin » Fri Nov 09, 2012 12:43 am

si-ghan-bi wrote:I tried bonnie++, useless. It generates the file(s) and then performs too short tests. I tried the option "-x n" …


Better use of options for bonnie++ are suggested under
ZFS-oriented benchmarking software suggestions (not results)
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Re: Benchmark/check L2ARC performances

Post by si-ghan-bi » Fri Nov 09, 2012 3:20 am

I used -r and -s as well, I was only pointing out that a proper test of L2ARC requires the software to reuse the files, otherwise there is no way to test the L2ARC, since the filling rate is constrained to a low value. I thought "-x n" would help, but it just start everything from scratch. Bonnie can help the testing of other types of performances, but just 4000 reads are definitely not enough for the L2ARC.

Now I am thinking about using IOmeter inside VirtualBox/Win8 or IOzone used multiple times while reusing the test files. I can let the tests run for a couple of hours and then check if the performances increase. It would be a replica of this benchmark:
http://www.zfsbuild.com/2010/07/30/testing-the-l2arc/
If the test file is exactly as big as the L2ARC, I can maybe get the results I want: maximum L2ARC performances to understand whether a USB stick is fast enough or not for that goal with my specific configuration.
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Re: Benchmark/check L2ARC performances

Post by grahamperrin » Fri Nov 09, 2012 9:18 am

Thanks – sorry for misunderstanding.
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arc_summary.pl

Post by grahamperrin » Thu Dec 20, 2012 1:52 am

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links

Post by grahamperrin » Thu Dec 20, 2012 10:14 am

si-ghan-bi wrote:Grahamperrin, would you please benchmark your system with and without USB stick als L2ARC? …


Without, with.
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Link

Post by grahamperrin » Wed Feb 06, 2013 5:39 pm

In Server Fault:


I thought I posted in the ZEVO support area about arcstat.pl some time ago, but can't find a matching post.

Things such as that .pl might not work with ZFS on OS X …
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Kingston DataTraveler 400

Post by grahamperrin » Wed Mar 27, 2013 2:50 am

si-ghan-bi wrote:Grahamperrin, would you please benchmark your system with and without USB stick als L2ARC? …


I shouldn't describe this as benchmarking but what it's worth, I do see occasional bursts of greater than average reads from the low-end device (Kingston DataTraveler 400) that's currently used as a cache vdev.

From a work in progress (the work is not L2ARC-oriented, but I caught sight of the burst):


This device typically shares a bus with nothing other than the iSight (MacBookPro5,2), which I rarely use:

2013-03-27 07-43-49 one of two USB 2 hi-speed buses.png
2013-03-27 07-43-49 one of two USB 2 hi-speed buses.png (209.71 KiB) Viewed 72 times


Note that I should not recommend this class of device for production purposes. (I'm testing, experimenting.)
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Re: Benchmark/check L2ARC performances

Post by raattgift » Thu Mar 28, 2013 7:53 am

One doesn't add an L2ARC for sustained-MB/s-from-the-L2ARC per se; they're for random-IOPS-from-the-L2ARC.

Mostly what you want to have in the L2ARC is warm zfs metadata, POSIX metadata, and small files (hot ones should be in ARC); all of these may be seeked to again at some point, robbing the pool of disk IOPS for very short reads. A solid state L2ARC, even one that is slow at writing and not too fast for reading, is still likely to remove seeks from seek-limited media (disks).

In most cases, disks (especially arrays thereof) will perform sequential reads at least as well as solid state L2ARCs, so therefore the L2ARC design (like the ARC one) tries to maximize the "sequentialness" of storage device activity. The cases where L2ARC has much more bandwidth than the pool it's attached to is easy to come by in Macs (a slice on an internal SSD makes for a fine L2ARC, and its sequential read bandwidth will be much greater than a set of disks attached via a single firewire bus. There is little to be done about that in the current ZEVO version, and in any case splitting a multi-disk pool across multiple external IO buses would be a greater win (writes benefit too).

In your case, the "not for production use" should really apply to USB2 at all. It is and always has been a source of tremendous problems for storage systems, including zfs, across many different OS platforms. ZEVO should outright warn people (via growl, even) when devices are attached via USB2.

(USB3 is OK, except for the occasions where USB3 devices attach as USB2 ones, devastating their performance and reliability).
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Thanks, and a link

Post by grahamperrin » Thu Mar 28, 2013 9:18 am

Thanks … makes sense. This helps me to plan for my next Mac – probably another MacBook Pro.

Postscript, cross reference:

USB 2.0 hub recommendations: Cerulian N14JB hub with a Kingston DataTraveler 400
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