On 01/23/2013 11:47 AM, Cousin Ricky wrote:
> James Holsenback <nom### [at] nonecom> wrote:
>>   In a /perfect/ world
>> RAID5 is a valid option.
>
> In a /perfect/ world, RAID would not be necessary at all.  Backups, neither.
>
>
LOL ... I didn't mean that quite so literally

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On Wed, 23 Jan 2013 10:09:00 -0500, Cousin Ricky wrote:

> My laptop is running on fumes. The battery is failing, and the Linux
> root partition has already gone south. I need a new computer.

I didn't realize there were others who crossed over from here to the 
Linux forums I admin (but I recognise your post from over there <g>).

I don't know that I'd worry too much about RAID - it tends to add 
expense, and most of the machines I've had for personal use have not used 
RAID for redundancy.  I /do/ back stuff up to an external 2 TB drive so I 
maintain two copies of the data that's important to me, and that's proven 
effective through multiple hard drive failures (oddly, mostly on the 
device that's backed up to rather than the "source" machines).  I've lost 
some non-critical data, but that's OK, because it was non-critical.

Cost of RAID has come down significantly with SATA/PATA RAID controllers 
in consumer-grade machines, but it still seems like overkill to me for a 
personal machine.  (My last home RAID system was a Compaq server-class 
486 that I bought in 1992 or so, and Compaq graciously gifted me a SMART 
controller and a couple of 2 GB drives in exchange for some volunteer 
work I did for them on CompuServe so I could run and support customers 
using their RAID controllers).

Jim

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On Wed, 23 Jan 2013 11:35:09 -0500, James Holsenback wrote:

> On 01/23/2013 10:41 AM, Le_Forgeron wrote:
>> Le 23/01/2013 16:09, Cousin Ricky a écrit :
>>> for Linux is most emphatically that RAID must not be used as a primary
>>> backup system.
>>
>> If you expect RAID to cover failure, you would be in for deception.
> 
> /generally/ speaking that would be false, but yep I agree with you on
> this, as I've seen failures involving two different mechanisms and
> recovery was problematic ... worst case scenario who be a failure that
> also involved loss of the parity compressed data. In a /perfect/ world
> RAID5 is a valid option.

Oh yes, I would agree as well.  The Compaq SMART controller I just 
mentioned in response to Ricky had multiple two-drive failures (caused by 
inadequate cooling at the end of the hardware's useful life).

Less likely is if you have a hot spare (which the newer SMART controllers 
supported 10 years ago) or mirrored RAID-5 (sometimes called RAID10, 
sometimes called RAID15 - there was no industry standard at the time for 
what it was called).

It's all about mitigating risk, and to do that, you have to consider MTBF 
and the environment the hardware is in (and how that is likely to affect 
MTBF).

Jim

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> My brother can't understand why I settle for an external backup disk. He says,
> RAID, RAID, RAID, all the way. He doesn't lose a keystroke after an equipment
> failure, and he sees no use for external backups.

It depends how much you value the work you would potentially lose 
between backups. For me personally I don't generate enough "work" on my 
home machine between backups (usually once per week) to justify the 
complexity, expense and education needed for running a RAID system. The 
other benefit of external backup is that you can take it to another 
machine very easily at any point. The other thing I do is to put a small 
number of critical files encrypted in a special folder that is then 
sync'd with a couple of online file storage sites. In case my HD and 
external fail together (eg huge power surge, house fire, flooding or 
some other disaster) then at least I don't lose the really important stuff.

> For the past decade or so, I have only used laptops at home. Power blackouts are
> frequent in my community, and laptops seemed the ideal way to get around that.
> However, my brother says that with my heavy computer usage, I should have a
> desktop system, and just buy a cheap laptop for traveling. Does this sound like
> a reasonable arrangement? I did have a battery backup, but it didn't take long
> for it to fail in my environment. Should I just resign myself to buying a new
> battery backup every couple of years?

Depends how often you get power outages, how long they are for and what 
you want to do on your computer during them. A powerful laptop running 
POV flat out will likely not even last an hour on battery, but if you 
just want email/web access you can get ones that will last 6 hours+. I'm 
happy with just a desktop because if there is a power outage I can still 
use my phone for web/email.

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Am 23.01.2013 16:09, schrieb Cousin Ricky:

> My brother is giving me the impression that he thinks external backups are a
> stupid idea. I don't feel comfortable without an external backup; however, if I
> do have an external backup, I don't see why I would need a RAID. Sure, without
> RAID, I can lose a few hours or a few days of work, but for my current
> (non-professional) needs, would that justify the extra expense of a RAID?

Think about it:

A RAID lets you continue work in case of a hard disk failure as if 
nothing had happened.

An external backup lets you restore most your data - but not the most 
recent stuff, and not in just a moment's notice - in case of a hard disk 
failure, a power surge that fries your whole computer, or - depending 
where you keep it - even a fire.

What's the thing you really want? What's the thing you really need? What 
are you willing to pay for it?

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Le 2013-01-23 14:30, Jim Henderson a écrit :
> Oh yes, I would agree as well.  The Compaq SMART controller I just
> mentioned in response to Ricky had multiple two-drive failures (caused by
> inadequate cooling at the end of the hardware's useful life).
>

If it's anything like the Compaq SMARTArray failures I've seen, the 
problem was EMI on the Proliand drive bay backplanes that made the 
controller receive garbled data, so it declared the disks bad, even 
though they were perfectly fine.  We had Compaq go and manually reset 
the disks to "good" status - using proprietary hardware - to recover 
some of the data after we had threatened to take our business elsewhere 
since we had had 7 or 8 RAID array failures in less than a month.

They also replace all our Proliant drive bays (60 of them, across North 
America) for a more recent revision number of the backplane.  Our 
carefull inspection revealed the "Rev. D" boards had two extra 
capacitors, and a huge ferrite core around the SCSI cable.

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I'm *certainly* no expert on RAID (in fact, I had to look up the modern meaning
of the term before posting this.) But from the comments here, and a quick
overview on Wikipedia, it seems to me that RAID arrays are really meant for
'professional' environments, where there is either a lot of data to constantly
backup, or the data is super-critical (from a business point of view.) Or the
user perceives it to be so. I do understand that some typical *home* users might
find such a thing beneficial for one reason or another; but the cost of external
backup drives--even multiple ones--is now so low (and the technical saavy needed
to use them is also low), that I'm curious as to RAID's practical use in a home
environment--given the OP's statement that the data he wants to backup is just
his typical home stuff. True, a RAID array allows instantaneous backup and
recovery of data AFAIU; but losing, say, only a week's worth of 'home' data
between (non-RAID) backups doesn't seem so terribly catastrophic. That's
debatable, of course!!

I suppose my opinion of this is based more than a little bit on my own
perception of the complexity of setting up a RAID array (in Windows), vs. using
simple external USB drives.

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Le 24/01/2013 15:57, Kenneth a écrit :
> I do understand that some typical *home* users might
> find such a thing beneficial for one reason or another; but the cost of external
> backup drives--even multiple ones--is now so low (and the technical saavy needed
> to use them is also low), that I'm curious as to RAID's practical use in a home
> environment--given the OP's statement that the data he wants to backup is just
> his typical home stuff.

Well, My home computer is loaded with 3TB of data (a few GB for the
system, all the remaining for audio, video, photos, emails & a bit of
povray... I do not want to bother managing the space: until I delete it,
I want to be able to retrieve it )

Backup on external virgin drive took more than 2 days to perform.
(and so far, I'm lucky, 3TB external drives do exist, and rsync is able
to continue from previous run)
updating backup (using rsync) take less time (but still a bit), but I'm
lazy so I do it once in a while. Nevertheless, I want to be protected
against a single drive failure (and as I do not want to manage the
space, I had to just see "one big space", so raid was already an option,
such as raid0 (concatenation of all disks as a single partition)).
So, instead of 5 disks, I bought a sixth one and setup a raid-5.
increase of disk prices is about the VAT, I can pay it twice for such
comfort... (and it was before the water over the factories in Asia, so
prices were even cheaper than a few months ago)

Now, would I split the backup across multiple backup drive ? Not as a
starter. I probably will have to do it one day, but it will bother me to
actually have to manage the directories (which one is big enough to fit ?).

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On Thu, 24 Jan 2013 09:12:26 -0500, Francois Labreque wrote:

> Le 2013-01-23 14:30, Jim Henderson a écrit :
>> Oh yes, I would agree as well.  The Compaq SMART controller I just
>> mentioned in response to Ricky had multiple two-drive failures (caused
>> by inadequate cooling at the end of the hardware's useful life).
>>
>>
> If it's anything like the Compaq SMARTArray failures I've seen, the
> problem was EMI on the Proliand drive bay backplanes that made the
> controller receive garbled data, so it declared the disks bad, even
> though they were perfectly fine.  We had Compaq go and manually reset
> the disks to "good" status - using proprietary hardware - to recover
> some of the data after we had threatened to take our business elsewhere
> since we had had 7 or 8 RAID array failures in less than a month.

The server was a Prosignia, but that's quite possible, too, I suppose.  I 
no longer have the system, but I do recall that the cooling in the room 
wasn't very good (it was my house, but the computer room was a southern-
facing room here in Utah, and the problems were always during the summer 
months).  Oh, and the power was intermittent in the system as well, so it 
could've been a bad PSU.

Jim

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On Thu, 24 Jan 2013 09:57:36 -0500, Kenneth wrote:

> I suppose my opinion of this is based more than a little bit on my own
> perception of the complexity of setting up a RAID array (in Windows),
> vs. using simple external USB drives.

Software RAID is certainly not a solution I'd use except in a pinch.  The 
overhead is too great.

HW RAID is a better solution, but also has its own issues with throughput 
bottlenecks (5+ drives on a single controller = massive need for 
bandwidth to the controller, and most don't have it, so your performance 
drops).

Jim

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