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Re: raid10 is killing me, and applications that aren't willing to wait for it to respond



On Wed, Dec 13, 2023 at 10:26:19AM -0500, gene heskett wrote:
> Greetings all;
> 
> I thought I was doing things right a year back when I built a raid10 for my
> /home partition. but I'm tired of fighting with it for access. Anything that
> wants to open a file on it, is subjected to a freeze of at least 30 seconds
> BEFORE the file requester is drawn on screen.  Once it has done the screen
> draw and the path is established, read/writes then proceed at multi-gigabyte
> speeds just like it should [...]

 - disk access latency
 - digikam
 - photo volume monitor
 - cache buffers (which?)
 - klipper

> I've been here several times with this problem without any constructive
> responses [...]

> So one more time: Why can't I use my software raid10 on 4 1T SSD's ?????

Gene, just a humble suggestion. I'm too short in time to wade through all
this deep software cake, of which I know but a fraction.

Perhaps if you structured your requests a bit better, the quality of the
answers would improve?

I've skimmed some of the answers, and they correspond to your confusing
request. Someone mentions DNS timeouts to rule them out right away (do
you access your RAID over the net? Is DNS resolution involved at all?)

Other answers veer of in similar disparate directions, but that corresponds
to your request's deeply confusing nature.

Let me humbly suggest to structure your search a bit (you do have deep
experience in fault searching, we all know).

What I get from your post is that you seem to see the root of your problems
in a long latency on (first?) storage access to your block device (whether
it matters that it be a RAID10 or a RAID42 we just don't know!).

This looks like a promising avenue, so let's pretend we start with this
one.

Do you experience this latency also with simpler tools (something which
doesn't "draw a requester on screen", like, say, ls or find)?

Let's thus try to rule out the deep pie of sh*** (uh, software stack)
you are using to access the disk. Do you still observe this latency?
Is there a pattern (like, when accessing something for the first time,
and/or accessing things after a longer inactivity period, yadda, yadda).

If yes, you can follow the path "disk access latency". If no, the problem
might lie further up the stack (and then, things like DNS latencies might
play a role again!).

With your posts, my head spins and my time slot in the mornings, before
I go to $DAYJOB is used up before I can start even to think about how
debug things.

In one short word: please focus. Debugging complex stuff becomes impossible
otherwise.

Cheers
-- 
t

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