"No O/S" after drive replacement with / on raid1

Hello.

I use 2 disks in mirror with root partition on softraid.
Say they are sd0a and sd1a and SR is sd2.
For example sd0 fails. I shutdown system, replace failed drive,
boot from good one, copy layout, rebuild array, all disks online
and system is up and running.
Then sd1 fails. I shutdown system, replace sd1, power on and...

Using drive 0, partition 3.
No O/S
_


Reading manuals, faqs and mailing lists led me to the following:
I reproduce the issue and after replacement first failed drive run
# installboot -v sd2

After that I can boot successfully from both drives.

Unfortunately I can not find this solution (is it a solution?)
neither in Disk Setup FAQ nor in lists.

I edited it for myself and here is diff for faq14.html.

##########################
$ diff -ur faq14.html.orig faq14.html
--- faq14.html.orig Sun Jan 31 20:12:36 2021
+++ faq14.html Sun Jan 31 21:45:55 2021
@@ -643,6 +643,23 @@
<a href="faq8.html#LostPW">single user mode</a>
or from the <a href="faq4.html#bsd.rd">install kernel</a>.

+<p>
+Also you advised to issue command:
+
+<pre class="cmdbox">
+# <b>installboot -v sd2</b>
+</pre>
+
+Otherwise in case if your second drive will fail this may lead you to
+
+<pre class="cmdbox">
+Using drive 0, partition 3.
+No O/S
+</pre>
+
+message after reboot
+
+
<h3 id="softraidFDE">Full Disk Encryption</h3>

Much like RAID, full disk encryption in OpenBSD is handled by the
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