On 7/30/26 18:17, Casey Deccio wrote:
On Jul 29, 2026, at 5:28 PM, Andy Smith<[email protected]> wrote:
...
If it does occur when /home is mounted, then it is the disks in the RAID
setup or the RAID setup itself. Does each individual disk perform
anomalously?
"fio" is a good tool,to carry out performance testing of storage
devices. Have a look what the random 4k read and write I/O is like in
terms of IOPS, and the sequential disk transfer rate in MB/s for reads
or writes. You can try that on the array and then break the array and
try it on each individual disk. Obviously this is destructive to the
data.
If the performance is as expected on a per-disk basis but terrible only
with RAID, it may be time to post to the linux-raid mailing list as this
is unlikely to be a Debian-specific issue. I would then also be checking
if it happens in other RAID configurations like RAID-1.
150 IOPS of random reads (not coming from RAM) is reasonable for a
single 7.2kRPM SATA disk. You could expect 2-3x this from a RAID-5 of
three identical disks.
Write IOPS is a bit more difficult to guess and will depend on whether
you have disabled the write cache in the drives themselves. Due to the
RAID-5 write penalty (read-modify-write) you may expect only 50-70% of a
single disk's IOPS for random writes.
Thanks for that very helpful information. I've run fio on the still-assembled
array, and here's what I get for read/write:
read: IOPS=237
write: IOPS=79
I'm not sure exactly what to make of that...
I might add insult to the injury, but are you sure you need RAID-5 if it
consists of just 3 drives?
Usually around 30% per drive's capacity will be sacrificed to hold error
correction data for the array,
so maybe it will be much better to use 2 drives in RAID-1 (Mirror)
configuration, if you need decent write performance.
Third drive could be used as spare device for the array, or a separate
storage without redundancy.
--
With kindest regards, Alexander.
Debian - The universal operating system
https://www.debian.org
