Roy Sigurd Karlsbakk wrote:
Hi all
I plan to setup a new system with four Crucial RealSSD 256MB SSDs for both SLOG
and L2ARC. The plan is to use four small slices for the SLOG, striping two
mirrors. I have seen questions in here about the theoretical benefit of doing
this, but I haven't seen any answers, just some doubt about the effect.
Does anyone know if this will help gaining performance? Or will it be bad?
I'm planning to do something similar, though I only want to install 2 devices.
Some thoughts I had so far:
- mirroring l2arc won't gain anything, as it doesn't contain any information
that cannot be rebuilt if a device is lost. Further, if a device is lost,
the system just uses the remaining devices. So I wouldn't waste any space
mirroring l2arc, I'll just stripe them.
- the purpose of a zil device is to reduce latency. Throughput is probably not
an issue, especially if you configure your pool so that large writes go to
the main pool. As 2 devices don't have a lower latency than one, I see no
real point in striping slog devices.
- For slog you need SSD with supercap which are significantly more expensive
than without. I'll try the OCZ Vertex 2 Pro in the next few days and can
give a report how it performs. For L2ARC cheap MLC SSDs will do.
So if I had the chance to buy 4 devices, I'd probably buy 2 different sets.
2 cheap large L2ARC devices, 2 fast supercapped small ones. The 2 slog devices
would go into a mirror, the L2ARC devices in a stripe. I'd probably take the
remaining space of the slog devices into the stripe, too, though this might
affect write performance.
Just me thoughts...
--
Arne
Vennlige hilsener / Best regards
roy
--
Roy Sigurd Karlsbakk
(+47) 97542685
r...@karlsbakk.net
http://blogg.karlsbakk.net/
--
I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er
et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av
idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og
relevante synonymer på norsk.
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