Re: suns raid-z / zfs

On Monday February 18, keld@dkuug.dk wrote:

On Mon, Feb 18, 2008 at 03:07:44PM +1100, Neil Brown wrote:

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On Sunday February 17, keld@dkuug.dk wrote:

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Hi

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It seems like a good way to avoid the performance problems of raid-5
/raid-6

I think there are better ways.

Interesting! What do you have in mind?

A "Log Structured Filesystem" always does large contiguous writes.
Aligning these to the raid5 stripes wouldn't be too hard and then you
would never have to do any pre-reading.

and what are the problems with zfs?

Recovery after a failed drive would not be an easy operation, and I
cannot imagine it being even close to the raw speed of the device.

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But does it stripe? One could think that rewriting stripes
other places would damage the striping effects.

I'm not sure what you mean exactly.  But I suspect your concerns here
are unjustified.

More precisely. I understand that zfs always write the data anew.
That would mean at other blocks on the partitions, for the logical blocks
of the file in question. So the blocks on the partitions will not be
adjacant. And striping will not be possible, generally.

The important part of striping is that a write is spread out over
multiple devices, isn't it.

If ZFS can choose where to put each block that it writes, it can
easily choose to write a series of blocks to a collection of different
devices, thus getting the major benefit of striping.


NeilBrown