[Tux3] "Intent logs" on separate device with tux3 ?

[Daniel Phillips]

On Thursday 12 March 2009, Michael Keulkeul wrote:
> Hi all,
> 
> Would it be possible to have a dedicated device for fast syncronious
> transactions, and latter flush to slower storage with tux3, or is this hard
> because of the design ?
> Sort-of copy the ZIL scheme of ZFS, and be able to recover all writes after
> a failover or a power loss.
> 
> Thanks in advance for your answers !
> 
> Michael B.

Hi Michael,

I expect Tux3 to be pretty fast for synchronous writes even without a
scheme like ZIL.  But if it were to be done, I would think a generic
virtual block device that implements a heirarchical cache would make
more sense than doing something special in the filesystem.

In general, I would like to view most of this "accelerate disk with
a small amount of expensive persistent storage" ideas as logical
volume manager problems.  Unsolved ones, to be sure, but no actual
reason for that.

As a volume manager solution, we could map part of the volume to fast
disk and most of the volume to normal, slow disk.  Then we always
allocate new writes into the fast disk area, and migrate those blocks
off somewhere else later (yes, Tux3 will have block migration).  A
good Master's thesis or two in there for someone.

Regards,

Daniel

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