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<p>On 8/21/19 1:23 PM, Jeff Frontz wrote:<br>
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<blockquote type="cite"
cite="mid:CAGvwsDmfyHg2iK8dvAOgpmBKGC9WWBvry5UB4SW-4w6vBkCzrg@mail.gmail.com">
<div dir="ltr">Does anyone have any success stories from using md?
How were you able to determine that it actually allowed the
system to successfully ride out a hard failure -- are there log
messages or anything that gave some indication?
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</blockquote>
<p>Yes.</p>
<p>I played around with md many years ago and it seemed to work
fine. I tried it on a couple of HDDs for learning purposes. I
also had a 4 port USB hub with 4 1 GB flash drives on it. I did
this because 4GB flash drives were really expensive and slow at
the time and 1 GB ones were getting cheap. But, mostly it was
because I am a geek and I liked to watch the lights flash with
different array types ;-)<br>
</p>
<p>Probably a year and a half ago my Cineraid 4 bay raid system
started flaking out and having write errors. Smartctl said one of
the drives had a corrected error. I bought a couple of new drives
for it (needlessly) and eventually determined that it was the
Cineraid that was bad and not the drives.</p>
<p>I didn't want to spend $200-$600 on a RAID enclosure. I bought a
wavlink 2 drive USB dock to go along with my old 2 drive Cineraid
dock. I setup md with raid-0, 5 and 10 (tried them all, just
playing) with 4 drives. It would occasionally get corrupted. I
tracked it down to when the 2 docks were turned on in a certain
order the kernel would bounce one of them and cause the raid to
fail.</p>
<p>I bought another wavlink dock and have been using 4 drives in a
raid-10 for probably 1.5 years. I also tried raid-0, 5 and
experimented with 6 drives. You can get SSD speeds, but the seek
time still lacks. I've used the commands to remove drives and
replace them and let them recover. I have also just purposely
pulled drives out of the dock, turned the power off on a cradle
and replaced them to make sure it works. You can set it up to
send you an email when a drive fails and it does send the email
immediately. It is also in the logs. You can cat /proc/mdstat to
watch the drives recover from a failure, or during the initial
create. There is also the mdadm command.<br>
</p>
<p>The one thing I had to do was make sure that the array is such
that set A is on one dock and set B is on the other dock. Once in
a long while USB will flake out (maybe I kick the cable) and it
will fail 2 drives. It always recovers painlessly. This isn't
server room reliability, but it suits my uses fine and was $40.<br>
</p>
<p>I also have 2 SATA SSDs in an md raid-0 array in my workstation.
They don't keep up with the 4x NVME drive, but they are quick. I
have never seen a problem with those.<br>
</p>
<p>Judd<br>
</p>
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