Commit fe11f3d0 authored by Mike Hibler's avatar Mike Hibler

Random neuron firings: thinking about how to image ZFS filesystems.

parent ec2565a8
......@@ -197,6 +197,32 @@ ENHANCEMENTS:
as well, but then we don't really save anything over just frisbeeing into
a tmp file and giving that to the next util in the pipeline.
Another approach can be used in the case where the -N "no decompress"
option is used. In fact, this is likely to be the common case for
something that is not an imagezip image. While we can "wrap" any file
as an imagezip image using the -f option of imagezip, there really
isn't any point. Examples of distribution of non-imagezip images are
tarballs/rpms and more interestingly, ZFS zsend streams. The latter
could be used to image ZFS filesystems--we save a zend stream, distribute
that via multicast, and use frisbee piped into zrecv to lay it down.
Anyway, when not decompressing we can be a little more opportunistic
when accepting out-of-order data. We can accept any chunks that fall
within the window covered by the number of write buffers we have.
E.g., if we have written to disk blocks 0-M and we have N blocks
worth of write buffers, we can accept any chunk that contains blocks
M+1 through M+N. Then we just change the writer thread to write blocks
in order and to block when it is missing anything.
10.Eliminate two levels of buffering in the "no decompress" case.
As distributing non-imagezip images becomes more common so does the
use of -N. When not decompressing, there is really no point in having
different chunk and write buffers, we might as well just use all the
space for chunk buffers and write directly from them when they fill up,
saving an extra copy of data. In addition to saving data copies, it would
make more efficient use of space.
PROBLEMS:
1. Have seen the clients run out of socket buffer space causing them
......@@ -209,5 +235,3 @@ PROBLEMS:
Assuming that we are getting it off the card in time, that means the
network thread is either not running frequently enough, or it is spending
too much time doing other things (like copying packet data, see #3 above).
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