KVM storage performance and cache settings on Red Hat Enterprise Linux 6.2

Written by Gionatan Danti on . Posted in Virtualization

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Debian base system installation time – EXT4 and guest-side write barriers enabled

While the previous test show remarkably well the situation when using relatively old guest filesystems, what happens when we use a modern, barrier-optimized filesystems as EXT4 inside our guest?

Debian install time - EXT4

Things become definitely more interesting: while slower, the writethrough setting regain competitiveness. However with guest-side write barriers turned on it isn't any more secure than the other caching methods.

Speaking between the nocache and write-back settings, we can see that the former has a slight edge in IDE mode: this is probably due to the “I-am-trying-to-use-host-cache-but-I-can't-really-use-it” situation in which the writeback mode find itself in this test (a .deb package installation is a mix of uncompressing and synchronized write to disk).

However, the two modes are more-or-less on par. This means that, when using a write-barriers aware guest filesystem, you can use one of these two settings, without boring with the slower write-through one.

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