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Re: ext3 Overhead


On Thu, 2004-02-19 at 21:25, Bodo Thiesen wrote:

> Most probably even more. Imagine deleting a directory recursively. On ext2 
> most unlink operations will cause only one write operation to disk. On ext3 
> each unlink operation creates at least one extra journal entry (plus the 
> write of the directory blocks).

That's true to some extent --- but remember that journal writes are
batched into big sequential IOs.  So for a whole 5 seconds' worth of
truncates, all of the separate bitmap updates for a single bitmap block
get coalesced; and then all of the separate pieces of metadata that were
touched are themselves coalesced into one journal IO.  And disk are
*MUCH* faster at sequential IO than random metadata IO.

So for embedded flash IOs, the overhead of the extra metadata IO is
significant, because flash doesn't (much) care about seeks.  But for
normal disks, the actual impact is very much less.


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