> Hey gang:
>
> Somebody mentioned the other day that UFS async isn't entirely async, and
> that directories are (always) sync. Is that true?
No.
The default is sync metadata and async user data, with the assumption
that the user will have taken a CS 203 class and know about two stage
commit for database/index integrity, if they care about their data.
With the "sync" option, all data, both metadata and user data, is written
synchronously.
With the "async" option, all data, both metadata and user data, is
written asynchronously.
Put another way:
default: A seat belt for you, but not the passenger
sync: A seat belt for you and your passenger
async: You are both strapped to the bumper
There's also soft updates. The point of soft updates is to ensure
ordering for maximal data ingrity (default ensures only metadata
integrity by ordering metadata operations, sync assures only that
writes occur in order, but that user data/metadata dependencies are
not assured because of implied dependecies between file contents,
and async implies no data integrity whatsoever).
Basically, soft updates is just a more efficient way of ensuring
operations occur in order (like the USL "DOW" -- Delayed Ordered
Writes -- technology, which is under patent, only more efficient).
So...
soft updates: A seat belat and an air bag for both you
and your passenger
Terry Lambert
te...@lambert.org
---
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