John McMonagle wrote:
Not saying its broke.
good :)
Part of my reasoning to go to raid5 was that I could expand.
OK that is really quite hard.
Unless you run lvm2 over the top - in which case it's a doddle (though constraints apply)
I'd do it anyway (run lvm2). It causes almost no performance issues and you can then grow your fs later.
You could build a raid5 then linearly extend onto a raid0
While it can be done I don't really see it as practical. Also it's looking like I probably will not need to expand.
Oh.
raid5 with 3 drives and 1 spare or 2 - 2 drive raid1 drives have the same space. Which is less likely to have a failure cause data loss? I'm guessing raid1. If I'm wrong I'd like to know now.
A 4x raid5 gives 3X space and survives 1 disk failure (a spare can be added later)
A 2x raid1/raid0+2 gives 2X space and if 1 disk fails then there's a 1/3 chance that a second failure will cause total failure.
A 3x raid5+1s gives 2X space and the ability for 2 simultaneous* disk failures
A 4x raid6 gives 2X space and the ability for 2 simultaneous** disk failures
* simultaneous here = apart from the few hours whilst a resync occurs - really I'm more interested in the lack of resilience during the few weeks whilst the RMA happens. Although I ended up with a spare 'cos I waited for a failure and bought a spare on next-day delivery whilst wrapping the failed disk for RMA
** really simultaneous
Also concerned about the resync times. It was going to take a couple days to resync under a rather light load if it weren't for the fact that it couldn't because of a bad drive and a kernel panic caused by the read error.
Hmm, took a few hours to resync 1Tb here. (maybe as much as overnight)
Still not certain about the cause of problem my current guess is the sata controller.
I run a 7 device SATA and it's81 stable (on 2.6.11.2 now).
I had a few minor problems a few months back but I think they've been sorted.
I'm glad there is work being done on the resync issue. Also think the ideas to attempt to fix read errors are great.
Yes the "read error = kick disk" is still a significant failing :(
My only suggestion is that there should be provision to send notification when it happens
such as this one:
This is an automatically generated mail message from mdadm running on cu.dgreaves.com
A Fail event had been detected on md device /dev/md0.
Faithfully yours, etc.
man madm (or Debian sets it up automagically)
HTH
One other suggestion is to consider using lvm over 2 raid1 devices rather than md0/md1 - I think you'll find a lot more flexibility there.
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