[Oberon] RFC: RAIF (Redundant Array of Independant Filesystems)

Dan Parnete dan.parnete at fastwebnet.it
Sun Jan 21 14:23:24 MET 2007

Patrick.Hunziker at unibas.ch wrote:
> Hi all:
> To solve some problems with data backup, I propose a RAIF (analogue to RAID)
> which stands for 'redundant array of independant filesystems' allowing
> transparent handling of identical files on two different filesystems. A nice
> feature would be that 'compressing file systems', 'remote file systems' etc can
> be neatly reused.
> Please comment this first draft critically, or improve directly the proposed
> implementation (which compiles, but is untested):
> Some features are not yet done (finalize, copy etc).
Excellent idea Patrik! A RAID, or RAIF as you call it, is what 
Bluebottle needs.
You intend RAIF more like a backup FS then a RAID, but it could be an 
important step too.

Some criticism:
1. The copy solution:
Coping the file at any Register could be useful  for a versioning 
system, but not for the AosFS. I have a customer database file of 1.3Gb 
and many others between 10-100 Mb, and they grow every day. The usually 
new added record is about 200-800 bytes for data records, and more for 
attached document files. Coping a 1.3Gb file for 800 bytes added will 
make the FS unusable.
I think the solution is not as simple, but you have to go deeper inside 
the I/O system.

2. Opening the most recent file of the two FS:
I should like to define witch FS is the main and with is the backup. All 
reading operations must be done from the main FS, otherwise we enter 
RAID territory and more other tasks must be implemented. If a file in 
the main FS is older then the backup one, an administrative error 
message must be triggered and an optional recovery/synchronization task 
could be started.

3. Incremental backup:
Could have sense in a daily backup procedure, but not at FS level (same 
reason as for point 1).

RAIF could be a very important first step to a real Bluebottle RAID 
implementation. If ETH intends to embrace such a solution, to define and 
coordinates it, but has no human resources for implementation, I am 
interested to participate to an open project.

Best regards,
Dan Parnete

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