On Wed, Apr 18, 2012 at 08:02:22PM +1000, Russell Coker wrote:
sure, that'll work. mdadm has no problem with multiple extra devices in a RAID-1. and reads should be amazingly fast.
It works for 2 disks, I've never had a reason to try with more.
I've tried it with three. it worked.
I wouldn't expect reads to be fast. Last time I tested such things I had great difficulty in demonstrating any read benefit for Linux Software RAID-1.
i didn't do any timing tests on three drives, so i'll take your word for it.
however, zfs works much better if you give it entire disks rather than partitions. [...]
Hmm, so it relies entirely on it's journalling to get consistent data? So what happens with an application calls fsync() or fdatasync()? How does ZFS know that the data is on disk?
I'll have to do some benchmarks of these things.
can't remember the details right now, and i'm kind of keen to go get some dinner :) try the zfsonlinux site: http://zfsonlinux.org/ see especially the ZoL github linked from there and the github issues.
making zpools from partitions does work, but is very strongly discouraged.
It sounds like ZFS will be more difficult than I thought. Do you have a reference for a good ZFS sysadmin guide?
i wouldn't say "more difficult" just some different factors to take into account when planning the server build. http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide http://www.solarisinternals.com/wiki/index.php/ZFS_for_Databases focused on solaris, but most of it is still relevant to zfsonlinux (and to zfs on freebsd too).
That sounds horrible, like a 1990's Linux install!
yeah, well, debian's installer doesn't support zfs yet. debian gnu/linux doesn't, debian gnu/kfreebsd does. if you want root on zfs you have to do some stuffing around. Six months ago I would have said don't bother - but from what i've read on the zfsonlinux sites, it sounds like it's pretty much sorted out now.
With a bit of luck the server I'll get will have an internal USB port. Then I can use a USB boot device. This is easy to setup and it's also easy to have a spare device just in case of corruption.
that would work too. some motherboards have internal USB ports for plugging USB drives inside the case. you can also buy jumper-block to USB port adapters off ebay for not much money. craig -- craig sanders <cas@taz.net.au> BOFH excuse #417: Computer room being moved. Our systems are down for the weekend.