Re: RAIDING different size drives

David Brown wrote
Rod Speed wrote
David Brown wrote
Rod Speed wrote
David Brown wrote
Rod Speed wrote
David Brown wrote

The extent to which your RAID offers protection depends on your failure recovery strategy.

Nope.

The benefits of *any* redundancy system are totally dependent on what happens when part of it fails.

Wrong. Mirroring is a useful protection against hard drive
failure regardless of what what happens when part of it fails.

Consider a setup like this:

Disk A, 750G:
partition 1, 250G
partition 2, 500G
Disk B, 500G:
partition 1, 500G

You put your OS, programs, etc., on "C drive" on partition A.1.
You mirror partition A.2 and B.1, and put your data on this "D drive".

Disk A dies.

You have a safe copy of all your data on the mirror B.1. But your OS drive is dead.

How do you get your data off B.1 again?

You reinstall the OS on the replacement drive and carry on
regardless. Not a shred of rocket science whatever required.

<snip>

Having no experience with windows software raid, I did not know if there were any complications involved (such as raid
setup information stored in the system registry).

That can obviously be backed up even if it is the case.

I did not know if there were likely to be risks involved, such as it being too easy to delete your good mirror by
making it part of a new raid, instead of rebuilding the raid. That's why I asked.

You initially proclaimed that there is no point in mirroring with Win.

That was just plain wrong.

But I am now happy to hear that recovery from failure in this situation is straightforward, and therefore this sort of
raid setup does offer useful protection.

If you are are not interesting in recovering when something has gone wrong,

Obviously the OP is.

you might as well backup to write-only media.

Having fun thrashing that straw man ?

There are a *lot* of people who effectively backup to write-only media

There arent really that many anymore. Essentially because write only media is so slow and of such limited capacity.

Perhaps you missed the point.

Nope.

"Write-only media" is media which cannot be read back, such as writing to unformatted tapes,

Which like I said, doesnt get used much anymore for home system backup.

or using encrypted backups without keeping track of the key.

Thats not write only media, thats a fucked up backup.

That's why testing your restore procedure is so vital - many people believe they
have good backup procedures, but have problems when they have to do a restore.

Thats much less common now than it used to be.

<http://www.linuxjournal.com/article/6435>
<http://en.wikipedia.org/wiki/Write_Only_Memory>

None of that is any news to anyone with a clue.

- I'm sure you've met plenty who think they have a good backup
system until the day comes when they need to do a restore.

Sure, but thats rather less common now.

But fair enough, it's a straw man here.

It is indeed.

Remember, I had originally made a suggestion of just using 500 GB
of the 750 GB for raid for storing data (see the details earlier in
this post). I know it's straightforward to access this data on a
Linux system even if drive with the OS has failed - you can boot a
live CD, and mount it directly.

You can with Win too.

How do you recommend doing a live Windows CD boot?

Barts is very convenient.

Its easier to use a Linux live CD for a Win system tho,
basically because it doesnt have to be built, just burnt.

I've seen some suggestions on the web, but they were mostly hacks of some sort.

Barts isnt.

If you know of a good way to make a general bootable windows CD with recovery tools, I'd be very interested.

Barts.

I find Linux live CDs useful for recovering problematic windows installations, but I'd be happy to expand my toolkit.

Barts is a lot more configurable and you can for example build a
bootable CD that includes various tools that you might need when
still working out what the hardware problem is if it isnt just a simple
hard drive failure etc or you prefer to continue to use the Win UI
when recovering instead of having to understand the basics of
Linux enough to be able to use that for the recovery.

There are others like the Ultimate Boot CD for Win that isnt strictly
speaking legal in the sense that some licensed software is included.
Corse you can always buy the licenses for whats included if you want.

So for Linux, it's a perfectly reasonable setup with a different
balance between efficient use of disk space and redundancy and uptime than you would get with a full drive raid.

But I'd like to be absolutely clear on this one - is it equally simple with Windows software raid,

Yes. And you can use a Linux live CD to do that too with Win.

If Linux live CDs can access windows software raid, then that's a good familiar safety net.

The main downside with that approach is that you do need to understand
the basics of Linux or choose a Linux thats very close to Win UI wise etc.

Even with a Linux thats very close to the Win UI, its not quite as convenient
to use the rather different UI with smartctl instead of say Everest which is
rather more convenient to use with a Win live CD to get a look at the state
of the hard drives when deciding what has died etc.

I think we have a slightly different idea of what the risks are regarding data

Nope.

- we have different backgrounds, different experiences,

Yes.

and different types of hardware, software, users, and data use.

Nope.

For my users, I don't expect to see any noticeable data loss if a
desktop harddrive dies. It means lost productivity, and an
inconvenience, but not data loss other than perhaps files that are
open at the time.

For home users without a server (with backup), I firmly believe
that using raid mirroring is of very little benefit compared to
spending the same money on a backup system

They arent alternatives.

(for home users, that typically means DVD writers, or perhaps an Internet-based backup system),

Nope. Most use external hard drives now.

or simply a second drive to which you make regular copies.

Anyone with a clue uses an external hard drive to reduce the risk of fire or theft etc affecting both drives.

Agreed - having the second disk external is much better (I think I mentioned that myself in an earlier post). It also
means it can be disconnected when you are not running backups (reducing wear on the disk, and risks of any user / OS /
malware issues), and you can easily connected it to another machine.

Copying to CD or DVD is still very popular - it's a familiar solution for many people.

And is very viable for backing up only the irreplaceable data
and being prepared to wear the extra effort of a full reinstall
in the very unlikely event of say a hard drive failure or fire etc.

And perhaps the use of internet-based backup is more common here in Norway than in many other parts of the world,
since we have a high percentage of users with fast (10 Mbit) broadband connections.

It isnt all that commonly used because much of the world
uses DSL that doesnt have that fast an upstream speed.

Very viable for incremental backup but not really that viable for full backups for most.

Either way, I don't think desktop raid is a big gain for data security.

Only in the sense that hard drive failure is uncommon.

Yes, hard drive failure is uncommon - especially in comparison to other causes of data loss such as user error.

Depends on the user.

I personally have a completely different backup scheme for code
with a high backup frequency manually initiated where I do another
copy of the current code at every major step in the process of writing
and modifying the code, to the same hard drive the code lives on,
with the code also included in the normal backup scheme as well.

That allows you to handle gracefully the all to common situation
where you decide a particular approach to the code will be useful
but it turns out to have a major downside that you didnt realise,
so you can step back to where you were before that sidetrack etc.

But clearly it does provide *some* gain - and if you already have a good backup system, then it adds a little more
(as well as speed and uptime benefits).

Thats just plain wrong with home systems.

The big advantage of mirroring when you already have decent backup is that it provides a useful extra level of
protection against hardware failure between backup runs.

OK.

Of course it mirroring improves data security, most obviously
with the new data that has showed up between backups.


.

Loading