Likely Readynas 3-series

janpeter wrote:
When I google on “btrfs raid5” I get the feeling that this in some implementations is not that well working and some fundamental development are going on. I see that the Linux Kernel version plays a role and some key improvement came with Kernel 3.19 but hard for me to judge this information, even though I searched our forum on kernel too.

Those articles are talking about the vanilla kernel found on kernel.org. Moving to a new kernel has its advantages and disadvantages.

janpeter wrote:
What Kernel does OS 6.2.4 have?

6.2.4 is using a 3.0.x kernel but it has a large number of BTRFS patches backported amongst other things.

The 6.3.x firmware (currently early access for the 300 series) uses kernel 3.12 again with a large number of BTRFS patches backported amongst other things.

A new kernel brings new features and other enhancements. There was an annoying bug present in early 3.19.x kernels. By steering clear of kernels while they are bleeding edge we can hopefully avoid most of the unexpected issues that a new kernel series brings and backport important fixes that are stable.

janpeter wrote:
I guess this link is relevant https://btrfs.wiki.kernel.org/index.php/RAID56 right?

We are not using the in-built BTRFS RAID. We are using md raid. We have a much more limited exposure to the RAID-5 write hole, since we use a transactional filesystem and we respect barriers. So we can get very close to doing atomic writes. We can also repair the data if just one chunk is out of sync. Our competitors are much, much, much more exposed.

janpeter wrote:
I guess raid1 is more “safe” sort of right now, but would be good to hear something that lessen my worries.

I'm using RAID-6 with my 516 and I'm comfortable with using that. We have users who have been using RAID-5 and RAID-6 since we first released our OS6 devices a few years ago.

janpeter wrote:
Closely related here is whether improvement for raid5 requires some hardware upgrade, or it is rather about firmware updates and fundamental ones like in the Linux kernel?

The RAID we use md raid is software RAID, this is very mature and we have been using it for a number of years. The in-built BTRFS RAID is also software based.

So a hardware upgrade will not be required to get improvements to the md raid we use. There may however be some hardware limitations e.g. for things like disk capacities supported. We can only guess as to whether higher capacities not available yet will work or not.