Dne 15.09.2020 v 10:22 Linda A. Walsh napsal(a):
On 2020/09/10 07:40, Miloslav Hůla wrote:
I cannot verify it, but I think that even JBOD is propagated as a
virtual device. If you create JBOD from 3 different disks, low level
parameters may differ.
----
JBOD allows each disk to be seen by the OS, as is. You wouldn't
create JBOD disk from 3 different disks -- JBOD would give you 3 separate
JBOD disks for the 3 separate disks.
Yes. If I create 3 JBOD configurations from 3 100GB disks, I get 3 100GB
devices in OS. If I create 1 JBOD configuration from 3 100GB disks, I
get 1 300GB device in OS.
So for your 16 disks, you are using 1 long RAID0? You realize
1 disk goes out, the entire array needs to be reconstructed. Also
all of your spindles can be tied up by long read/writes -- optimal speed
would come from a read 16 stripes wide spread over the 16 disks.
No. I have 16 RAID-0 configurations from 16 disks. As I wrote, there was
no other option of how to propagate 16 disks as 16 devices into OS few
years before.
What would be better, IMO, is going with a RAID-10 like your subject
says, using 8-pairs of mirrors and strip those. Set your stripe unit
for 64K to allow the disks to operate independently. You don't want
a long 16-disk stripe, as that's far from optimal for your mailbox load.
What you want is the ability to have multiple I/O ops going at the same
time -- independently. I think as it stands now, you are far more likely
to get contention as different mailboxes are accessed with contention
happening within the span, vs. letting each 2 disk mirror potentially doing
a different task -- which would likely have the effect of raising your
I/O ops/s.
The reason to not create RAID-10 in controller was, that btrfs scrubbing
detects slowly degrading disk much sooner than controller (verified many
times). And if I create RAID-10 in controller, btrfs scrub detects soon
too, but I'm not able to recognize on which disk.
Running raid10 on top of raid0 seems really wasteful
I'm not doing that.
