On 2016-08-30 11:32, Richard Brown wrote:
On 30 August 2016 at 11:09, Carlos E. R. <> wrote:
I assume you mean btrfs with RAID 5/6. Software raid with any other filesystem is Ok, right?
Ok is a matter of perspective.
All RAID 5/6 implementations, including hardware ones, are at risk of a 'write hole', when something interupts the write. When this happens, the parity information doesn't match the rest of the data for the stripe.
Ah, ok, but this is not new.
For hardware raid this is typically only during a power outage. Software RAID has an increased chance of this happening, due to increased opportunities for something to interupt that write, such as a kernel crash.
Yes, fair enough :-)
Hardware RAID arrays mitigate this risk by using either non-volitile caches or battery backups to allow the writes to complete even in the event of a power outage.
Software RAID has no such mitigations.
Aha, yes. Still software raid has some advantages over fake hardware raids, in the the home (server) scenario. I was not considering serious implementations, with real hardware cards that include a battery backup. (For the record, I have always been against raid in home(server) scenarios. I advise instead people to dedicate the extra disk(s) for backups. I think that many people misunderstand what raids are for.)
So, RAID 5/6 always comes with an element of risk. A high-end hardware controller with NV cache and theoretically 'perfect' firmware has little risk. A well maintained hardware controller with a sysadmin regularly taking care that the battery is working has a small risk. and then it increases from there.
Understood.
And the btrfs RAID 5/6 implementation is probably the least safe of all the software RAID options available on openSUSE (and is therefore not available on SLE).
This is the new factor :-)
But I personally wouldn't recommend any software RAID 5/6 of any type on any openSUSE filesystem for anyone who want to ensure their data is consistant and stays that way.
But nothing new in this area. Nothing like "debacle over RAID 5/6" that Lindsay mentioned. Or is he referring to a new implementation of raid? :-? I thought I heard of a raid implementation peculiar to btrfs. -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)