Re: NetBSD Raid5, slow write speeds, using big disks?!

Thanks Dave, i will most likely have a look at Raid10, which according to wikipedia is two raid1 and one raid0:
raid1a - disk1,disk2
raid1b - disk3,disk4
raid0 - raid1a,raid1b

And might look into raid5 with 3 disks as Greg suggested.
Funny thing is, that i can swear i looked for like best raid config for 4 disks 6 months ago and raid5 was suggested... :D
Would be nice if wikipedia had some rough estimates of speed, like your single drive has X as write speed. Raid0 will have X write speed, raid5 X/4, raid10 X/2 or something like that...

Br Nicklas


On 6/22/26 9:05 PM, Dave B wrote:
> If you decide to stay away from ZFS, it still might be best, as I
> understand it, to avoid RAID 5 specifically, unless your system
> has a hedge against the "RAID 5 write hole".  (Acknowledgment: not
> an original opinion on my part; rather, advice which, over the
> years, already gets posted to this list from time to time, IIRC).
>
> I'm not claiming to be a RAID or RAIDframe expert, so I won't try
> to explain the "write hole"; but suffice it to say that after
> experiencing enough problems with RAID 5 (on less-than-rock-solid
> hardware & in potentially flakey power-environments), my life was
> improved by deciding to stop using it...  This was on big "-ish"
> disks at the time, though probably an order of magnitude smaller
> than your current ones.
>
> I believe RAID 1, RAID 10 & RAID 6 either don't suffer from
> "write hole" issues or at least are less susceptible to them.
> [I'd recommend confirming this via more reliable sources; not
> stated here as fact].  So RAID 1 is what I now stick with on
> RAIDframe generally, and I also use hardware RAID 10 & RAID 6 on
> systems with applicable controllers.
>
> Building on previous remarks that a 4-drive set-up isn't optimal
> for RAID 5, it's worth adding that 4-drive set-ups *are* nicely
> conducive to RAID 10 & RAID 6, and more feasible to align with
> stripe & buffer size; though wouldn't include any hot-spares.
>
> The "cons" of RAID 10 & RAID 6 (compared to RAID 5) are that they
>
>   - will only offer you ~14TB total storage (rather than your 4-
>     drive RAID 5's ~21TB)
>   - and AFAIK aren't directly supported by RAIDframe
>     - however, RAID 10 can be achieved by raidframe-on-raidframe,
>       at the slightly cumbersome cost of setting up & managing
>       three raidN devs (a RAID 1 of two RAID 0's -- or maybe a
>       RAID 0 of two RAID 1's, I forget which is RAID 10 & which is
>       RAID 01...)
>
> The "pros" of RAID 10 are that it
>
>   - will still survive the loss of 1 drive, just like RAID 5; and
>     in uncommon cases, even that of 2 drives.  I wouldn't bank on
>     the latter, however
>   - should be *really fast* for both reads & writes (comparatively
>     speaking)
>
> The "pro" of RAID 6 is that it will survive loss of 2 drives,
> provided you can get it working with RAIDframe... although I
> believe it would be comparatively slow.
>
> The above is all stated from perceptions & recollections, my
> apologies if I have any errors in, e.g., objective facts.  Again,
> best to confirm anything critical your data might depend on from
> more official sources.
>
> Best, -D