SATA JBODs for backup-to-disk

Arno Wagner wrote:
Well, then you should adjust your language to the standards that cover
this, unless you want to be misunderstood. JBOD does mean "Just a
Bunch Of Disks", but "Just a Bunch Of Disks" is a RAID mode
also known as SPAN, concat or append mode.

A reference:

http://en.wikipedia.org/wiki/Standard_RAID_levels


You're going to quote Wikipedia to me as an authorative source? Well, I
can show you a site just as authorative that says differently.

What is JBOD? - A Word Definition From the Webopedia Computer Dictionary
"Just a Bunch Of Disks Used to refer to hard disks that aren't
configured according to RAID -- a subsystem of disk drives that improves
performance and fault tolerance."
http://www.webopedia.com/TERM/J/JBOD.html

Previously Yousuf Khan wrote:
Arno Wagner wrote:
Well, then you should adjust your language to the standards that cover
this, unless you want to be misunderstood. JBOD does mean "Just a
Bunch Of Disks", but "Just a Bunch Of Disks" is a RAID mode
also known as SPAN, concat or append mode.

A reference:

http://en.wikipedia.org/wiki/Standard_RAID_levels


You're going to quote Wikipedia to me as an authorative source? Well, I
can show you a site just as authorative that says differently.

No. I am giving you one reference that explains it and I am telling
you that what is there is the common usage. There is no authorative
siurce as of now, as with a lot other CE/CS terms. But there is common
usage. Vendor brochure usage does not count, vendors will mangle terms
to an arbitrary degree if they think something sounds cool. Just
think of Windows XP. XP means "experimental", period. It has been
meaning that for decades and comes from airplane model designations.
But for MS it means "experience" and they have zero justification
for it.

What is JBOD? - A Word Definition From the Webopedia Computer Dictionary
"Just a Bunch Of Disks Used to refer to hard disks that aren't
configured according to RAID -- a subsystem of disk drives that improves
performance and fault tolerance."
http://www.webopedia.com/TERM/J/JBOD.html

Well, that is incomplete but not really add odds with the Wikipedia
definition, now is it? They just stress a bit more that JBOD
does not have redundancy in a bit nebulous way. Whether you want to
call JBOD (or RAID0 for that matter) a RAID mode or not, is a
matter of taste. The ''R'' is certainly not in them. But if
you relax on the ''R'', then RAID0 and SPAM/APPEND/JBOD are
both RAID modes.

Arno

Arno Wagner wrote:

You're going to quote Wikipedia to me as an authorative source? Well, I
can show you a site just as authorative that says differently.



No. I am giving you one reference that explains it and I am telling
you that what is there is the common usage.


I would not say this is "common usage". I've been using JBOD's for many
years and they have mostly had nothing to do with RAID. If you get an
enclosure full of drives it is either a RAID unit or a JBOD. The only
cross-over has been with the 3Ware RAID cards where if you want to use a
drive by itself, not part of a RAID set, then you specify it as a JBOD
drive.

Whether you want to
call JBOD (or RAID0 for that matter) a RAID mode or not, is a
matter of taste. The ''R'' is certainly not in them. But if
you relax on the ''R'', then RAID0 and SPAM/APPEND/JBOD are
both RAID modes.


JBOD has no "A" in it either. They are not part of an array. No one disk
has anything to do with any of the other disks. That is the whole idea
of JBOD's (as far as I have ever heard).

Steve Cousins wrote:


Arno Wagner wrote:

You're going to quote Wikipedia to me as an authorative source? Well,
I can show you a site just as authorative that says differently.


No. I am giving you one reference that explains it and I am telling
you that what is there is the common usage.

I would not say this is "common usage". I've been using JBOD's for many
years and they have mostly had nothing to do with RAID. If you get an
enclosure full of drives it is either a RAID unit or a JBOD. The only
cross-over has been with the 3Ware RAID cards where if you want to use a
drive by itself, not part of a RAID set, then you specify it as a JBOD
drive.


Expansion enclosures for raid storage systems are usually JBOD, they get
their RAID capabilities from the controller in the main enclosure. So
it's a bit too simple to say that JBOD is only used in applications
without RAID.



--
Nik Simpson

Nik Simpson wrote:

Steve Cousins wrote:



Arno Wagner wrote:

You're going to quote Wikipedia to me as an authorative source?
Well, I can show you a site just as authorative that says differently.



No. I am giving you one reference that explains it and I am telling
you that what is there is the common usage.


I would not say this is "common usage". I've been using JBOD's for
many years and they have mostly had nothing to do with RAID. If you
get an enclosure full of drives it is either a RAID unit or a JBOD.
The only cross-over has been with the 3Ware RAID cards where if you
want to use a drive by itself, not part of a RAID set, then you
specify it as a JBOD drive.



Expansion enclosures for raid storage systems are usually JBOD, they
get their RAID capabilities from the controller in the main enclosure.
So it's a bit too simple to say that JBOD is only used in applications
without RAID.

Sure they can be used in RAID applications. I use them for software RAID
all the time. But there is nothing about them being JBOD that implies
RAID. That RAID people use JBOD's doesn't mean that the term JBOD
implies RAID.

Arno Wagner wrote:
Previously Yousuf Khan wrote:
You're going to quote Wikipedia to me as an authorative source? Well, I
can show you a site just as authorative that says differently.

No. I am giving you one reference that explains it and I am telling
you that what is there is the common usage. There is no authorative
siurce as of now, as with a lot other CE/CS terms. But there is common
usage. Vendor brochure usage does not count, vendors will mangle terms
to an arbitrary degree if they think something sounds cool. Just
think of Windows XP. XP means "experimental", period. It has been
meaning that for decades and comes from airplane model designations.
But for MS it means "experience" and they have zero justification
for it.

I worked for a reseller of storage systems for years, and that is the
first time I've ever even heard of JBOD being described as another term
for concatenation. To me there was never any confusion about the term,
nor any hint that the term was under confusion, until this discussion.

What is JBOD? - A Word Definition From the Webopedia Computer Dictionary
"Just a Bunch Of Disks Used to refer to hard disks that aren't
configured according to RAID -- a subsystem of disk drives that improves
performance and fault tolerance."
http://www.webopedia.com/TERM/J/JBOD.html

Well, that is incomplete but not really add odds with the Wikipedia
definition, now is it? They just stress a bit more that JBOD
does not have redundancy in a bit nebulous way. Whether you want to
call JBOD (or RAID0 for that matter) a RAID mode or not, is a
matter of taste. The ''R'' is certainly not in them. But if
you relax on the ''R'', then RAID0 and SPAM/APPEND/JBOD are
both RAID modes.


Read the discussion forums in the Wikipedia entry about that JBOD term.
It is being described as being completely wrong by most of the
discussees. I will be editing that definition from Wikipedia in a few
days when I have some time. It's completely wrong.

Yousuf Khan

Steve Cousins wrote:
Whether you want to
call JBOD (or RAID0 for that matter) a RAID mode or not, is a
matter of taste. The ''R'' is certainly not in them. But if you relax
on the ''R'', then RAID0 and SPAM/APPEND/JBOD are
both RAID modes.


JBOD has no "A" in it either. They are not part of an array. No one disk
has anything to do with any of the other disks. That is the whole idea
of JBOD's (as far as I have ever heard).


That Wikipedia entry is completely f*ked up, it's time to change it.

Yousuf Khan

Nik Simpson wrote:
Expansion enclosures for raid storage systems are usually JBOD, they get
their RAID capabilities from the controller in the main enclosure. So
it's a bit too simple to say that JBOD is only used in applications
without RAID.


It's very simple, if you can see and control the disks individually in
the OS, then they are JBODs. If the OS just sees the volume and not the
underlying disks, then it's not JBOD.

Yousuf Khan

Previously Yousuf Khan wrote:
Steve Cousins wrote:
Whether you want to
call JBOD (or RAID0 for that matter) a RAID mode or not, is a
matter of taste. The ''R'' is certainly not in them. But if you relax
on the ''R'', then RAID0 and SPAM/APPEND/JBOD are
both RAID modes.


JBOD has no "A" in it either. They are not part of an array. No one disk
has anything to do with any of the other disks. That is the whole idea
of JBOD's (as far as I have ever heard).


That Wikipedia entry is completely f*ked up, it's time to change it.

Change the rest of the explanations on the web as well, while you are
at it.

Arno

"Yousuf Khan" wrote in message
Arno Wagner wrote:
Previously David Boyer wrote:
If you lose one disk, you shouldn't lose everything IF the JBOD is
configured properly. You can usually use mirroring, RAID 5, RAID 6, and RAID
10, and any other methods you would use to survive one or more disk
failures.

JBOD is a RAID mode. It just places the individual disks sectors one
after another and supports differently sized disks. JBOD is not
RAID 1/5/10 or any other redundant RAID level. JBOD is sometimes
called APPEND mode (e.g. by the Linux LVM).

Depending on the JBOD vendor, the array config is stored on each
of the physical disks, so you can remove a disk or diskset and pop it in a
year later and have it back online just by installing the drives. We've been
doing backups to a 6TB SATA JBOD for nearly two years, and it works great.
The problem with our JBOD is that drives are hot-swappable, but aren't
otherwise designed to be modular.

Maybe you mean something else than the Just a Bunch Of Disks RAID
mode here?


To me, JBOD means "Just a Bunch Of Disks". That's a system where
each of the individual disks is visible to the operating system in their
raw individual disk form, rather than visible to the OS as a virtual
volume pre-virtualized by a hardware RAID disk array. JBODs can
then be volumized by software RAID into concats, stripes, mirrors,
RAID 5, and other RAID modes.

Pity then that even the OP had something quite different in mind when he
mentioned "JBOD":

"We know there are a lot of vendors offering SATA JBODs
*with either FC or Ultra320 interfaces*"

"Depending on the *JBOD vendor*, *the array config* is stored on each
of the physical disks, so you can remove a disk or diskset and pop it
in a year later and have it back online just by installing the drives".

Obviously his 'JBOD's have internal array controllers.


Yousuf Khan