What happens to discs in a JBOD 'raid' array when one crashes.

[Marcel Overweel]

JBOD isn't RAID but it is mentioned a lot with RAID controllers.
I found the following text on the net:

"A lot of people talk about JBOD and disk spanning as being
considered forms of RAID. This is not really true; JBOD stands
for Just a Bunch Of Disks and its purpose is to combine
multiple hard disks into one. It does not provide redundancy,
and therefore is not technically a level of RAID. However, JBOD
is useful if you have an application that requires mass amounts
of contiguous hard disk space and you don't have a large drive
to use. This should only be used as a band-aid fix though, as
several drives combined leads to increased chances of failure."

So what is the risk if one drive failes?
Do I lose the whole array?

The reason I ask: I am not concerned about data safety.
I have a server just as a data store for a media streamer.
Everything stored on that server is also backed-up on cd's
and dvd's.

But if it means that, if one drive fails it ruins the whole array,
I'd rather not use jbod at all.
(I'm talking about 6TB of data and I don't want to copy
*everything* if 1TB drive failes.)


regards,
Marcel

 

[Mike Walsh]

JBOD is used where each disk is used for a different purpose e.g. one for each OS, one for data, one for the page file, etc.. They can do double duty e.g. the drive with the OS can be used to backup data files from the disk with the working data. JBOD does not usually involve an array, but you could use software RAID to span disks.

 

[Marcel Overweel]

That would be a multi-drive span. You can do that with
typical raid controllers, OR instead you could do single
drive spans which is the same as what a non-raid controller
on any motherboard does, sometimes with the exception of
writing metadata which is only used for identification
purposes, typically with single drive spans it just
identifies it is an existing volume, not a newly added drive
that should be flagged for input from the system
administrator for some designation of purpose for the
drive... and yet typically a newly added drive that is not
designated at all, defaults to single drive span. Just
don't manually set it to single drive stripe as this makes
it's access proprietary to the raid controller used to set
it up (or one intercompatible with that controller which is
still fairly limiting).





6TB is way too much to be backing up with DVDs, IMO, let
alone CDs. Consider either tape or hard drives for backup.

I think I used the wrong words here, this server is for
mediastreaming only, so all that's going to be put on the
drives is already stored somewhere else.
Mostly on DVD's.

If one drive fails I do think you lose the whole array in
practical terms of it being readily accessible for use, but
at least unlike RAID0, there is in theory a good chance a
disk scanning type of recovery software could salvage some
if not all of the data remaining on the viable drives. I
wrote "in theory" because I have never recovered data from a
JBOD, would never use one. You should do a test by copying
test data, actually unplugging a member then seeing if you
can recover from it in a timely fashion.

Yeah, that's a good idea. I can copy a huge zip or rar file over
and over again each with a different name and see what
happens if one drive gets unplugged.

In the case of wanting a lot of hard to manage (for recovery
due to size) data intact I would use RAID5 instead. That
incurrs the cost of a more elaborate RAID controller if
yours doesn't support it, and needing one addt'l drive
compared to what you would've needed for JBOD, but having
the ability to recover gracefully from a single drive
failure makes it seem the best option in your situation.

I will look into that as well. I'm fairly new with raid and jbod
did sound very interesting because for the mediastream
it is impossible to point to more than four sources.

Options, options

Thanks kony!

regards,
Marcel

 

[Marcel Overweel]

ok, thanks!

regards,
Marcel

JBOD is used where each disk is used for a different purpose e.g. one for
each OS, one for data, one for the page file, etc.. They can do double
duty e.g. the drive with the OS can be used to backup data files from the
disk with the working data. JBOD does not usually involve an array, but
you could use software RAID to span disks.