[TriLUG] B320i RAID controller driver

[Joseph Mack NA3T via TriLUG]

On Fri, 22 May 2020, Matt Flyer via TriLUG wrote:

> Wasn't planning on spending any money, just want to re-purpose what I
> have in the best means available.

fair enough.

> There are some disadvantages with RAID.

well it's more complicated that's for sure. Mirroring is simplest.

> A coworker says that he likes RAID 6.

everyone (well the people who can't have downtime, or data failures) likes RAID 
6. You need two disks to fail before you loose your filesystem. Since most 
people running RAID have large file systems, rebuilds can take a long time, in 
which the disks are being hammered by both the regular users and the rebuild. 
People worry that under this stress, another disk on the way out can fail too.

(I assume your setup isn't being hammered by the users, so you can expect a 
rebuild so go smoothly.)

> I thought though that RAID 1+0 uses two mirrored pairs with each pair having 
> half the blocks. Consequently, it would take two drive failures, of the same 
> pair, in order to lose data. 

yes.

>> In your setup with 4 disks, I would have two mirrored pairs and mount them 
>> so  that they make up your whole filesystem.


> Good point. Are you suggesting making two mirrored pairs and then say
> logically calling them SDA and SDB?  An LVM type file system or similar
> could spread the partitions across them.

I'm a little worried by what you might be thinking when you say "spread the 
partitions across (the disks)"

Let's assume you have two disks (no mirroring) and you use (say) mdadm to make a 
single file system out of them, with size=sum of the two disks. Let's say one 
disk fails. The blocks on the OK disk are useless, because files will have been 
spread over both disks. I don't know where the inodes etc go; they may not be on 
the working disk you have. You want when a disk dies, not to take any other 
disks down with it. Instead put / and /usr on one disk and /data (or /home or 
whatever) on the other disk. Thus when one disk goes down, the other disk is 
still useable.

In your case, just mirror both of these disks.

> As it stands, I disabled the hardware RAID controller and Linux install medium 
> can now see the 4 disks.

hooray.

>  Choices, choices when it comes to the setup.

Joe

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Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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