Re: "Virtual" RAID1

[Brett Lymn <blymn%internode.on.net@localhost>]

On Mon, Jun 24, 2019 at 10:38:17AM +0200, tlaronde%polynum.com@localhost wrote:
> 
> I have read the presentation of the features (I have a copy of a book on
> AFS that I need to read to), so it has features that I'm after but it
> lacks also one feature: the reality of disks and the need for
> dissymmetry: RAID1 puts an equal burden on both disks meaning that to
> serve one data, you stress two disks; whether you put two high end
> server's disks---and it is a waste---or youp put two desktop/terminal
> disks, and you will spend your time replacing disks praying that they
> not both die at the same moment.
> 

well you would be pretty unforutnate for that to happen and, besides, in
backups we trust ;)

> I have in mind a simple block upon which one could imagine building
> distributed data.
> 

Have you looked at glusterfs?  It sounds like you may be trying to
implement something like that.

> 
> One can see that distributed file system and disconnection can be
> handled with this element: since writes (depending on filters) is always
> duplicated, in one member is a "local" storage, there is always (if not
> discarded by filter) a local copy of written data on the node. So if the
> other component is a remote file service, the disconnected client can
> work.
> 

OK, so you then have to make some hard decisions on how you handle
performance.  Are you going to choke write performance to the slowest
disk or have some sort of buffering to hide the write delay.  If you
rely on syncing of the mirror components then you still can lose data if
the up-to-date component fails before the mirror sync is done.

-- 
Brett Lymn
--
Sent from my NetBSD device.

"We are were wolves",
"You mean werewolves?",
"No we were wolves, now we are something else entirely",
"Oh"