On 07/02/10 11:14, Erik Trimble wrote:
On 7/2/2010 6:30 AM, Neil Perrin wrote:
On 07/02/10 00:57, Erik Trimble wrote:
That's what I assumed. One further thought, though. Is the DDT is
treated as a single entity - so it's *all* either in the ARC or in
the L2ARC? Or does it move one entry at a time into the L2ARC as it
fills the ARC?
It's not treated as a single entity but at a block at a time.
Neil.
Where 1 block = ?
I'm assuming that more than on DDT entry will fit in a block (since
DDT entries are ~270 bytes) - but, how big does the block get?
Depending on the total size of the DDT? Or does it use fixed-sized
blocks (I'd assume the smallest block possible, in this case)?
- Yes, a pool block will contain many DDT entries. They are stored as a
ZAP entries.
I assume but I'm not sure if zap blocks grow to the maximum SPA block
size (currently 128KB).
Which reminds me: the current DDT is stored on disk - correct? - so
that when I boot up, ZFS loads a complete DDT into the ARC when the
pool is mounted? Or is it all constructed on the fly?
- It's read as needed on the fly.
Neil.
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