«

As hard drives get larger and larger, more and more RAID configurations
become no longer worth using. Nobody should be using RAID 5 any more. RAID
10 may still be worth something, but for how long?

<http://blogs.zdnet.com/storage/?p=483>

Roll on the next-generation filesystems ...

On 2009-05-20, Lawrence D'Oliveiro <_zealand> wrote:
> As hard drives get larger and larger, more and more RAID configurations
> become no longer worth using. Nobody should be using RAID 5 any more. RAID
> 10 may still be worth something, but for how long?
>
><http://blogs.zdnet.com/storage/?p=483>
>
> Roll on the next-generation filesystems ...
>
Meanwhile, as he says make 3 copies of the data which is valuable to you

In message <>, Gordon wrote:

> Meanwhile, as he says make 3 copies of the data which is valuable to you

RAID isn't about backups.

"Lawrence D'Oliveiro" <_zealand> wrote in
message news:gv0i99$uto$...
> In message <>, Gordon wrote:
>
>> Meanwhile, as he says make 3 copies of the data which is valuable
>> to you
>
> RAID isn't about backups.
>

But good backups will enable you to recover your critical data from
the RAID failures he is talking about.

Alan.

--

The views expressed are my own, not those of my employer or others.
My unmunged email is: (valid for 30 days
min probably much longer).

"Allistar" <> wrote in message
news:8tudneBJj_g5-...
> Lawrence D'Oliveiro wrote:
>
>> As hard drives get larger and larger, more and more RAID
>> configurations
>> become no longer worth using. Nobody should be using RAID 5 any
>> more. RAID
>> 10 may still be worth something, but for how long?
>>
>> <http://blogs.zdnet.com/storage/?p=483>
>>
>> Roll on the next-generation filesystems ...
>
> RAID isn't so much about file systems, it's about either performance
> (by
> parallelising reads) or redundancy (in case a disk dies).
>
> I don't see how a new file system will help if the disk dies.
>

Do we even need a new file system?

Consider this (I've tried to simplify the arrangement so no comments
on whether this would be a USEFUL arrangement please!):

If I have three physical disks (let's assume 750GB each for ease of
calculation) and use a hardware RAID controller to set them up in
RAID5.

I now have what the OS sees as a single 1500GB disk.

If I now have the OS 'split' that into three virtual disks of 500GB
each, and have the OS create a software RAID5 array across those three
virtual disks, then I now have what the user / apps see as a single
1000GB disk.


Now, if one of the physical disks dies and gets replaced, the hardware
RAID would rebuild that from the parity info on the other two physical
disks.

If it runs into an URE and cannot rebuild one of the sectors, that
sector is lost completely. Okay.

However, if we consider the software RAID, this will manifest itself
as a sector on ONE (?) of the three virtual disks having been lost or
damaged (experienced an URE), but this is not fatal since it can
rebuild that sector from the parity information on the other two
virtual disks.


Is that correct, or am I missing something?

Thanks,

Alan.

--

The views expressed are my own, not those of my employer or others.
My unmunged email is: (valid for 30 days
min probably much longer).

On May 20, 7:03*pm, Lawrence D'Oliveiro <l...@geek-
central.gen.new_zealand> wrote:
> As hard drives get larger and larger, more and more RAID configurations
> become no longer worth using. Nobody should be using RAID 5 any more. RAID
> 10 may still be worth something, but for how long?
>
> <http://blogs.zdnet.com/storage/?p=483>
>
> Roll on the next-generation filesystems ...

RAID is nothing to do with file systems....RAID is about read/write
performance and some online survivability in the case of a RAID
failure....you are a fool if you dont do backups....and effectivly at
>2TB you are not likely to recover any time soon.....

regards

Thing

On May 21, 9:36*am, "Alan" <a...@alan.invalid> wrote:
> "Lawrence D'Oliveiro" <l...@geek-central.gen.new_zealand> wrote in
> messagenews:gv0i99$uto$...
>
> > In message <77i05iF1hbij...@mid.individual.net>, Gordon wrote:
>
> >> Meanwhile, as he says make 3 copies of the data which is valuable
> >> to you
>
> > RAID isn't about backups.
>
> But good backups will enable you to recover your critical data from
> the RAID failures he is talking about.
>
> Alan.
>
> --
>
> The views expressed are my own, not those of my employer or others.
> My unmunged email is: *1bupdv...@sneakemail.com (valid for 30 days
> min probably much longer).

The problem is disks are getting so big that backup media is failing
to match it as a sane cost and recovery time....

About the only "sensible" costed system is backing up disk to disk....

regards

thing

In message <b8b42384-ac42-41a7-b6af-
>, wrote:

> On May 20, 7:03 pm, Lawrence D'Oliveiro <l...@geek-
> central.gen.new_zealand> wrote:
>
>> As hard drives get larger and larger, more and more RAID configurations
>> become no longer worth using. Nobody should be using RAID 5 any more.
>> RAID 10 may still be worth something, but for how long?
>>
>> <http://blogs.zdnet.com/storage/?p=483>
>>
>> Roll on the next-generation filesystems ...
>
> RAID is nothing to do with file systems....RAID is about read/write
> performance and some online survivability in the case of a RAID
> failure....

It's that "survivability" that's looking increasingly in doubt as drives get
larger. And next-generation filesystems include such survivability in their
design, in a more scalable way. They can probably also take care of the
performance issue while they're at it.

"Lawrence D'Oliveiro" <_zealand> wrote in
message news:gv24p9$saj$...
> In message <b8b42384-ac42-41a7-b6af-
> >,
> wrote:
>
>> On May 20, 7:03 pm, Lawrence D'Oliveiro <l...@geek-
>> central.gen.new_zealand> wrote:
>>
>>> As hard drives get larger and larger, more and more RAID
>>> configurations
>>> become no longer worth using. Nobody should be using RAID 5 any
>>> more.
>>> RAID 10 may still be worth something, but for how long?
>>>
>>> <http://blogs.zdnet.com/storage/?p=483>
>>>
>>> Roll on the next-generation filesystems ...
>>
>> RAID is nothing to do with file systems....RAID is about read/write
>> performance and some online survivability in the case of a RAID
>> failure....
>
> It's that "survivability" that's looking increasingly in doubt as
> drives get
> larger. And next-generation filesystems include such survivability
> in their
> design, in a more scalable way. They can probably also take care of
> the
> performance issue while they're at it.
>

Hi Lawrence,

Did you see my question above about layering two RAID configs (h/w and
s/w) on top of each other?

Is that a solution?

Alan.

--

The views expressed are my own, not those of my employer or others.
My unmunged email is: (valid for 30 days
min probably much longer).

Alan wrote:
> "Lawrence D'Oliveiro" <_zealand> wrote in
> message news:gv0i99$uto$...
>> In message <>, Gordon wrote:
>>
>>> Meanwhile, as he says make 3 copies of the data which is valuable to you
>>
>> RAID isn't about backups.
>>
>
> But good backups will enable you to recover your critical data from the
> RAID failures he is talking about.
>
Not necessarily. If the mode of failure is that the disk is readable but
not writeable, you could be thinking that you had written something to
it and not actually been able to. Then when the backup comes along, it
reads the wrong data and carefully stores it on tape.

Cheers,

Cliff

--

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