Re: RAIDING different size drives

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). 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.

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. "Write-only media" is media which cannot be read back, such as writing to unformatted tapes, or using encrypted backups without keeping track of the key. 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.

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


- 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? I've seen some suggestions on the web, but they were mostly hacks of some sort. If you know of a good way to make a general bootable windows CD with recovery tools, I'd be very interested. I find Linux live CDs useful for recovering problematic windows installations, but I'd be happy to expand my toolkit.

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.


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 and 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 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.


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.

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.


.

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