geom_raid5 inclusion in HEAD?
olli at lurza.secnetix.de
Thu Nov 15 07:14:33 PST 2007
Arne Wörner wrote:
> Oliver Fromme wrote:
> > Just a small question: I noticed that the new gvinum
> > raid5 implementation (in P4) allows adding disks to an
> > existing RAID5, even while it is running. Does geom_raid5
> > support that, too? (ZFS doesn't, unfortunately.)
> Nope... graid5 doesnt do such things... I found no way, that could do it
> without hurting the disks too much (I was afraid, that a power failure could
> destroy the necessary knowledge about the size of the new-config-area; and I
> didnt know how to do the beginning: it seemed like the first few blocks need a
> special treatment, because there the new-config-area and the old-config-area
OK. I don't know the inner workings of geom_raid5, so I
can't tell how difficult it would be to implement there.
Here's a little description and some ASCII graphics that
explin how growing RAID5 was implemented in the new
> But Veronica is developing a tool, that can do it in offline mode... With
> service interruption...
> But growfs induces a service interruption anyway and it is buggy, if u do
> not zero the new area... Veronica filed a bug report about this...
Hm. I used growfs only once, and it worked fine. Was
there a regression introduced at some point? It should
certainly be fixed, because growfs seem to be very
About service interruption: growfs only takes a few
seconds, which might be acceptable in most cases.
But taking a whole RAID5 down to add disks and then
rebuilding it takes a _lot_ longer. Therefore I think
the feature to add disks to a live RAID5 would be very
> Nowadays it is common practice to have 2 ot more hosts, that can substitute
> each other (hot-standby or how they call it today), so that it doesnt matter,
> if a box is damaged or in maintenance mode or... isnt it?
It depends. Building a fail-over cluster with FreeBSD
is not trivial if you need a synchronized, consistent and
reliable file system on all of the nodes.
Of course you can use third-party black boxes such as
a cluster of NetApp Filers or whatever. That would work
(I've put such setups into production myself), but it
costs a non-negligible amount of money, and it's
certainly not suitable for everyone.
YMMV, of course.
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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