Re: [PATCH 0/4] 3- and 4- copy RAID1

[waxhead <waxhead@dirtcellar.net>]

David Sterba wrote:
> An interesting question is the naming of the extended profiles. I picked
> something that can be easily understood but it's not a final proposal.
> Years ago, Hugo proposed a naming scheme that described the
> non-standard raid varieties of the btrfs flavor:
> 
> https://marc.info/?l=linux-btrfs&m=136286324417767
> 
> Switching to this naming would be a good addition to the extended raid.
> 
As just a humble BTRFS user I agree and really think it is about time to 
move far away from the RAID terminology. However adding some more 
descriptive profile names (or at least some aliases) would be much 
better for the commoners (such as myself).

For example:

Old format / New Format / My suggested alias
SINGLE  / 1C     / SINGLE
DUP     / 2CD    / DUP (or even MIRRORLOCAL1)
RAID0   / 1CmS   / STRIPE
RAID1   / 2C     / MIRROR1
RAID1c3 / 3C     / MIRROR2
RAID1c4 / 4C     / MIRROR3
RAID10  / 2CmS   / STRIPE.MIRROR1
RAID5   / 1CmS1P / STRIPE.PARITY1
RAID6   / 1CmS2P / STRIPE.PARITY2

I find that writing something like "btrfs balance start 
-dconvert=stripe5.parity2 /mnt" is far less confusing and therefore less 
error prone than writing "-dconvert=1C5S2P".

While Hugo's suggestion is compact and to the point I would call for 
expanding that so it is a bit more descriptive and human readable.

So for example : STRIPE<num> where <num> obviously is the same as Hugo 
proposed - the number of storage devices for the stripe and no <num> 
would be best to mean 'use max devices'.
For PARITY then <num> is obviously required

Keep in mind that most people (...and I am willing to bet even Duncan 
which probably HAS backups ;) ) get a bit stressed when their storage 
system is degraded. With that in mind I hope for more elaborate, 
descriptive and human readable profile names to be used to avoid making 
mistakes using the "compact" layout.

...and yes, of course this could go both ways. A more compact (and dare 
I say cryptic) variant can cause people to stop and think before doing 
something and thus avoid errors,

Now that I made my point I can't help being a bit extra hash, obnoxious 
and possibly difficult so I would also suggest that Hugo's format could 
have been changed (dare I say improved?) from....

numCOPIESnumSTRIPESnumPARITY

to.....

REPLICASnum.STRIPESnum.PARITYnum

Which would make the above table look like so:

Old format / My Format / My suggested alias
SINGLE  / R0.S0.P0 / SINGLE
DUP     / R1.S1.P0 / DUP (or even MIRRORLOCAL1)
RAID0   / R0.Sm.P0 / STRIPE
RAID1   / R1.S0.P0 / MIRROR1
RAID1c3 / R2.S0.P0 / MIRROR2
RAID1c4 / R3.S0.P0 / MIRROR3
RAID10  / R1.Sm.P0 / STRIPE.MIRROR1
RAID5   / R1.Sm.P1 / STRIPE.PARITY1
RAID6   / R1.Sm.P2 / STRIPE.PARITY2

And i think this is much more readable, but others may disagree. And as 
a side note... from a (hobby) coders perspective this is probably 
simpler to parse as well.