On 2020-02-21, Nick Holland <n...@holland-consulting.net> wrote:
On 2020-02-20 11:22, Oliver Marugg wrote:
Hi
I’ve got a Supermicro 5028D desktop server with 5 identical
SATA SSDs,
there is no HBA no RAID card in. The purpose of the server is
intended
as web/smtp and some vmm vms (os plus /home & /var storage).
What are your suggestions or best practices configuring the device
arrangement (eg. sofraid(4), bio(4),bioctl(4) OS 2x on 2x ssd raid1,
data 3xssd raid5 or 1x single ssd for OS and 4x ssd raid5/10 or
better
ideas)?
You came in a bit late with the question (i.e. after you already had
the
hardware!).
IMHO there's little use for RAID5 these days. The advantage is "more
storage from a given number of drives". But that can more easily be
fixed by using larger drives which are easier to recover in the
event of failure.
I'm not sure what level of support softraid has for stacked
disciplines
(it doesn't have direct RAID10 support). The boot loader only supports
RAID 1 and crypto, so you will either want RAID 1 on the boot drives,
or boot from USB stick etc.
I think the only options that really make sense for OpenBSD are
2-drive RAID1 for main OS, and then either 2-drive RAID1 for data,
plus
a single drive for an extra copy of important things (I hesitate to
use
the word 'backup' for something in the same machine, but sometimes it
can be helpful to have something that is easier to restore than your
actual backups ;) - though for such a setup I would have gone with
HDD rather than SSD for the 5th drive - or 3 single drives for data.
set it up as you need it...
If you think your description is anything close to specific for
specific
recommendations, you need to get out more. Everything you said could
vary in demand by many orders of magnitude, except for the model
number
the server...a curious thing to be specific about.
E-mail is one of those things that's really hard to get a good backup
of, as it changes minute by minute and is considered fairly
important,
Dovecot replication (dsync) does a pretty good job of this actually.
I think it's a much better idea than trying to backup mailboxes on an
active system. Either run periodically to alternative storage on the
same machine, or preferably to a different machine (preferably in a
different building).
so I'd consider a three disk RAID1 for the mail store, as a disk
system
failure invariably means "lost data", even with frequent backups.
Three disk RAID1 gives you a simple disk structure that can tolerate
a disk failure and still provide redundancy. (some people will tell
you that RAID1 is only two disks. These people are wrong, but often
include HW RAID controller makers. Three disk RAID1 examples are in
the man pages).
Since these are SSDs and apart from random hardware failures (which
aren't
*so* common) the main failure mode is doing too many writes. So with
three
disk RAID1 the main thing you end up doing with 3 mirrored SSDs is
wearing
out three drives rather than two with writes at the same rate.
The other risk is data corruption (either on the bus or on storage
either over time - "bit rot" - or firmware bugs etc). softraid doesn't
have anything to help with this (even for detection, let alone
figuring
out which copy of the data, if any, is correct).
As for the rest...it's a matter of how much space you need and how
much down time you can tolerate, and how you are set up to deal with
that downtime. And I'm assuming you aren't combining external and
internal services on one box. I suspect that's a bad assumption.
And even after much careful analysis it's a bit of a guess.
Sometimes you guess wrong. So keep your design flexible and be
willing and able to say, "Well, this isn't working, let's rebuild
it with the knowledge we now have". This idea that you have to have
the perfect build the first time out is ... well, just wrong.
yep :)
