On Wed, 7 Jan 2009, Dmitry Koterov wrote:
Hello.
Suppose I perform 1000 RANDOM writes into a file. These writes are saved
into Linux writeback buffer and are flushed to the disc asynchronously,
that's OK.
The question is: will physical writes be performed later in the sequence of
physical SECTOR position on the disc (minimizing head seeking)? Or Linux
background writer knows nothing about physical on-disc placement and flushes
data in order it is saved in the RAM?
E.g., if I write in the application:
a) block 835
b) block 136
c) block 956
d) block 549
e) block 942
dows the Linux background writer save flush them e.g. in physical order "136
- 549 - 835 - 942 - 956" or not?
yes, the linux IO scheduler will combine and re-order write requests.
they may end up being done 835-942-956-549-136 if the system thinks the
head happens to be past 549 and moving up when the requests hit the IO
system.
David Lang
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