Some ZFS+NFS benchmarks (OpenSolaris)

Bernd Walter ticso at
Wed Feb 24 01:39:28 UTC 2010

On Tue, Feb 23, 2010 at 10:21:41PM +0100, Ivan Voras wrote:
> On 23 February 2010 20:34, Bernd Walter <ticso at> wrote:
> > On Tue, Feb 23, 2010 at 08:15:48PM +0100, Ivan Voras wrote:
> >>
> >>
> >> It's curious how ZIL on SSD doesn't help them with NFS when they
> >> increase the load.
> >
> > My assumption is because they already write linear on SSD and get a more
> > or less fixed write rate, while parallel write rate with disks can
> > increase because of reordering.
> >
> > I'm personally impressed by my own tests on how much our current
> > USB stack can speed up random reads even with cheap USB flash sticks
> > used as cache devices.
> This is surprising to hear - I've just run some randomio
> ( tests on two little used USB
> flash sticks and got around 110 IOPS sequential writing (~~ 7 MB/s)
> and a bit less than 30 IOPS random writes of 4 KB buffers (amounting
> to ~~ 1 MB/s).

Yes - your values seem to fit with my assumed values, but I'm talking
about L2ARC cache devices here.
Those are written linear with small bandwith and read random.
If they are too slow ZFS just drops data and cache fill slower.
Random read access for USB sticks is great compared to HDD - although
USB has a high latency overhead.

> (the test command was "randomio file 16 1 1 4096 10").
> The ZIL should be written practically linearly - the sequential write
> rate is relevant here - and it is actually significantly slower than
> what mechanical HDDs can achieve.

A small test with ZIL on USB sticks was horrible because it couldn't
take up with write speed.

> Is your result with ZIL perhaps simply because you moved it to another
> device and so freed the main device?

I assume for ZIL you really need a device with fast write speed, but
I have not much experience with ZIL devices.

B.Walter <bernd at>
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.

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