Re: Disk I/O slowness

On Tue, Aug 04, 2026 at 02:00:05PM -0400, Stefan Monnier wrote:
>So overall the circumstances where raid 5/6 makes sense are a small
>minority.  It's mostly for cases where total capacity is a lot more
>important than performance and even there, the benefit is only 33% in
>your scenario (8GB vs 6GB).  And when total capacity is a lot more
>important than performance one would typically go for HDDs (where the
>performance impact of raid 5/6 tend to be even more pronounced).

That depends on what you mean by "performance". A large (8 or more 
drive) RAID-6 is going to have similar performance to RAID-10 for random 
or sequential reads (operations will be balanced across drives). For 
sequential writes the RAID-6 will likely be faster. Random writes will 
be worse on the RAID-6, but a write cache will hide much or all of that 
depending on the details of cache size, write size, etc. And with larger 
numbers of drives the difference in overhead becomes more significant. 
(50% usable for RAID-10, 75% for 8 drive RAID-6, 83% for 12 drive 
RAID-6.) And a last really important feature: RAID-6 can tolerate *two* 
failed drives in an array without losing data. With RAID-10 if a drive 
fails during a rebuild, the array is done. And rebuilds can take a 
*long* time (like, days). You can get double disk failure tolerance on 
RAID-10, but then you're down to 33% usable space.