----- Original Message -----
> On 04/25/11 11:55, Erik Trimble wrote:
> > On 4/25/2011 8:20 AM, Edward Ned Harvey wrote:
> > > And one more comment: Based on what's below, it seems that the DDT
> > > gets stored on the cache device and also in RAM. Is that correct?
> > > What
> > > if you didn't have a cache device? Shouldn't it *always* be in
> > > ram?
> > > And doesn't the cache device get wiped every time you reboot? It
> > > seems
> > > to me like putting the DDT on the cache device would be harmful...
> > > Is
> > > that really how it is?
> > Nope. The DDT is stored only in one place: cache device if present,
> > /or/ RAM otherwise (technically, ARC, but that's in RAM). If a cache
> > device is present, the DDT is stored there, BUT RAM also must store
> > a
> > basic lookup table for the DDT (yea, I know, a lookup table for a
> > lookup table).
> No, that's not true. The DDT is just like any other ZFS metadata and
> can be split over the ARC,
> cache device (L2ARC) and the main pool devices. An infrequently
> referenced DDT block will get
> evicted from the ARC to the L2ARC then evicted from the L2ARC.
and with the default size of a zfs configuration's metadata being (ram size -
1GB) / 4, without tuning, and with 128kB blocks all over, you'll need some
5-6GB+ per terabyte stored..... -- 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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