On 08/17/16 07:49, Slawa Olhovchenkov wrote:
On Wed, Aug 17, 2016 at 07:36:00AM -0700, Nathan Whitehorn wrote:
Your contention that the installer does not make policy decisions is
equally spurious. The installer makes many policy decisions, including
the disk layout, the size of the swap partition, the name of the pool,
the use of boot environments (which I dislike but am not allowed to
override), the number of filesets and their mountpoints (which I also
dislike and am not allowed to override either), etc. The Unix
philosophy is to push such decisions up the stack, not down. The
decision to align partitions on 4096-byte boundaries because we're not
sure of the correct number but know for a fact that using a smaller
number can have a huge impact on performance is the installer's to make.
Those are all things that the operating system does not have defaults
for: there are no tools like, say, gpart or newfs that layout disks in
any even vaguely automated way, and so no tools that would ever have
defaults for, say, the size of a swap partition except for the
installer. As such, the defaults are quite properly in the installer.
This is quite different: there are many tools that care about disk
alignment (say, gpart) and, by default, use the GEOM stripesize. The
installer is, after this patch, overriding what was meant to be a
system-wide default.
My concern is that pushing this into the installer means that newfs,
zfs, gpart, etc., which all look at the GEOM stripesize for preferred
alignment, will still have suboptimal behavior on systems affected by
your patch. If we identified which drivers are reporting the wrong
alignment, we could fix the whole system at a go by changing it there.
As it is, we now have inconsistent default behavior for partitions
between tools (the installer and sade will now use a different alignment
than gpart on whatever systems you were trying to fix here) and between
pre- and post-installation environments.
In long term, prefered aligment is forsing 4k (or may be more):
install system on 512b [mirror] disk aligment now may be need required replace
disk to 4k aligment. For more flexsible in future now best chois is 4k
or more.
For future-proofing in such circumstances, it might be worth expanding
the vfs.zfs.min_auto_ashift tunable into some global thing that the disk
drivers (or geom_disk) read to round up the physical sector sizes they
would otherwise report. That would ensure that gpart, zfs, etc. all
behave consistently in such cases.
-Nathan
_______________________________________________
svn-src-head@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
