On 3/7/24 14:06, Segher Boessenkool wrote:
On Thu, Mar 07, 2024 at 09:28:13AM -0800, Bart Van Assche via cfarm-users wrote:
On 3/7/24 01:30, Martin Guy via cfarm-users wrote:
which usually begins to degrade above 80% and seriously above 90% if
I remember correctly.
I think that there is a significant difference between log-structured
and overwrite-in-place filesystems with regard to performance if a
filesystem is almost full. I think the above numbers come from the
following paper: Rosenblum, Mendel, and John K. Ousterhout. "The design
and implementation of a log-structured file system." ACM Transactions on
Computer Systems (TOCS) 10, no. 1 (1992): 26-52.
Disks were 50MB..150MB in those days.
Although I know that we are digressing since gcc110 does not use a
log-structured filesystem, isn't the conclusion from that paper that
disk utilization should be kept below 80% for log-structured
filesystems independent of the disk size? Since every SSD implements a
log-structured filesystem internally I looked up a paper about SSD
internals. This paper also includes a graph that shows that utilization
should be kept below 80%: Hu, Xiao-Yu, Evangelos Eleftheriou, Robert
Haas, Ilias Iliadis, and Roman Pletka. "Write amplification analysis in
flash-based solid state drives." In Proceedings of SYSTOR 2009: The
Israeli Experimental Systems Conference, pp. 1-9. 2009
(http://roman.pletka.ch/publications/hu2009write-ampl.pdf).
Bart.
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