On Wed, 17 Oct 2012, Russell Coker wrote:
On Wed, 17 Oct 2012, Peter Ross <Peter.Ross@bogen.in-berlin.de> wrote:
http://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html
"Block Devices (Are Gone)" ;-)
That sounds bogus to me. Despite the lack of the BSD split device model we manage to not lose data on Linux. I think that they are advocating a BSD design flaw as a feature.
I think the main reason is KISS. FreeBSD does not have block devices, /proc, /sys, does not rely on hald and dbus and whatever was invented on Linux - and I don't miss it.. Security-wise it makes a difference if you have multiple entry points to whatever it is.
It would probably be much the same in that they are both strings of bytes managed by the same ZFS code. Of course a file has mtime and atime fields while a block device probably doesn't.
There is "zfs set atime=off" but I don't think you can disable changing mtime.
I could imagine using LVM on Dom0 and giving partitions to the DomUs and running ZFS inside.
That means you lose the contiguous write feature of ZFS which is essential to good performance. Ext3/4 on LVM volumes gives somewhat contiguous reads where possible, ZFS when it owns the disks gives contiguous writes, but ZFS on multiple LVM volumes gives neither.
Agreed. Easy administration vs. performance.
Multiple ZFS instances is not "easy administration" IMHO. ZFS is a bit of a pain to setup, once it's going it makes some things easier, but it's not as easy as other filesystems. It's not something you do mkfs ...; mount ...
I don't know. I am doing "zfs create" and "zfs set mountpoint" all the time, and the number of machine tweaks isn't that high, mainly restricting the ARC size, or disabling prefetch. But: ZFS is memory hungry, and if you have multiple DomUs, you would have all of them sharing the physical RAM, and next to nothing is shared amongst them. So you probably don't want to have many DomUs with ZFS on the machine. Regards Peter