Re: blocksize > 4K in ext2 ?

Mark H. Wood (mwood@mhw.OIT.IUPUI.EDU)
Thu, 21 May 1998 12:57:36 -0500 (EST)

On Thu, 21 May 1998, Rik van Riel wrote:

> On Wed, 20 May 1998, Sieger Ralf AI wrote:
> > I currently developing a fs which supports among other things
> > fragmentation. This means for better throughput I want to use the highest
> > possible blocksize. So if someone has an solution to this limit I would
> > cheer.
> It's simple. Use 4kB blocks for I/O, and use multiple blocks
> for on-disk allocation.
> ie:
> - you do I/O in multiple 4kB chunks
> - you allocate disk space per 256 4kB chunks
> This way, you have 1MB disk blocks. And if you use the
> ext2fs preallocation scheme, you can even free the 4k
> blocks which aren't used by the file when the file is
> closed...

What do you do with the freed 4k blocks? Novell has one answer --
somehow they "suballocate" this unused space, packing several small files
into a single block. When free blocks run short, though, the machine
goes into a tailspin looking for spare sub-blocks and does very little
else. (Axe one big file and your responsiveness comes right back...once
your delete request get serviced.)

Mark H. Wood, Lead System Programmer   mwood@IUPUI.Edu
Nothing is so dangerous as being too modern.  One is apt to grow old-fashioned 
quite suddenly.  -- Oscar Wilde

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