Mirroring vs Raid

Good point. Too bad all boards use compatible controllers.

Digerati said:

I'm not a big proponent for using RAID 1 (mirrors) at home.

The use of RAID1 here just allows your OS to keep running in the event of a hard drive failure.

I disagree. While I do agree everyone should have a viable backup plan, the use of RAID1 at home makes perfect sense in the event a hard drive fails. Without RAID1, a drive failure means total data loss and for many, the data is MUCH more valuable than the OS and hardware. Without RAID1, the only chance of recovery from a drive failure is a backup - which most people don't use, or don't keep very current.

With a home machine, I think it's far less problematic if you have to take the machine down for awhile while you reinstall your OS or restore an image that you made and then put your data back.

Oh? Have you ever had a drive fail in RAID1 array? I have and simply pulling the bad and inserting a new drive and letting the controller do the rest (while you keep on computing barely losing a stroke) is FAR LESS problematic than pulling the old drive, inserting the new, resinstalling Windows, drivers, all your security programs, all the updates, and then restoring your data from the most recent backup. It is definitely less problematic than restoring from an image file - which is not likely to be current.

And as for backups - a RAID1 provides a very easy method of having a fairly current backup. Just swap in the spare drive every week, and put the removed (now the spare) drive in a safe place - like a bank safety deposit box. Then next week, swap them again, they sync and become current and you are good to go.

Intriguing. Can I do that with Windows 7's mirroring through E-sata? I probably can but how many mirrors can I have?

I plan on having two drives in mirror and a third one for backup. I paid a good ~$400 for data recovery in the past year so I'd rather spend that money on the actual hardware than to the recovery company. Just last week my 1 terabyte disk failed. No sweat as I had it on a Hardware Raid 1 but until I get the replacement drive through warranty, I risk data loss. So I am thinking of weekly backups of a raid 1'ed array.

I am not in the US btw and over here at the moment an external e-sata 1.5tb and an internal sata 1.5 tb have ~5$ difference in price. So I am thinking on getting external drives as they come with a box that protects the drive from shock to a degree.

My problem with the method you described is that opening the case weekly or monthly is too much of a chore and I would probably drop the disk on that one occasion.

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To rewind to my original question and perhaps revise it... I plan on migrating to software raid (windows 7 mirroring) from my hardware raid that comes with my motherboard. I see that this will give me liberty from my hardware without a serious performance lost (and perhaps a gain).

Would you support my method of using the mirroring function to slowly migrate away from motherboard based hardware raid?

On an unrelated note, how does windows 7 react to when the main disk that other disks are mirroring is gone? Can I declare a mirror to be primary?

White Cat said:

I probably can but how many mirrors can I have?

Not sure what you mean by how many mirrors. A typical RAID1 uses two drives - they mirror each other. The spare drive is not mirrored, until it is swapped in. You can certainly have many spare drives and swap them in any time you wish.

My problem with the method you described is that opening the case weekly or monthly is too much of a chore and I would probably drop the disk on that one occasion.

This is where hot-swappable drive bays with external access is nice - but these are not normally found on home systems. What I have seen some folks do is mount the spare in the case, then simply swap the cables between the spare and the on-line every so often. I personally don't like that idea because if the computer is stolen, or there's a fire or flood, you lose the spare (and the data on it) too. The best backup solution involves saving a copy in a safe place off-site.

As far as opening your case, note you should be inspecting the interior of your computer at least monthly anyway, and clean out the heat-trapping dust when needed.

If you have two external e-SATA ports controlled by the same RAID controller, it should work and be much easier to swap spares. I can't answer about Windows 7's mirroring. I don't use it.

Just last week my 1 terabyte disk failed. No sweat as I had it on a Hardware Raid 1 but until I get the replacement drive through warranty, I risk data loss.

This is why the spare should be "on-hand" - so you can swap it in right away. But note when setting up a RAID, you should buy all the drives at once, including the spare or spares. In this way you can ensure you get identical drives - same model AND revision number. Not all controllers can support mis-matched drives. This becomes important 2, 3, 5 years down the road, when the drives start to age, and the makers have retired those models.

pparks1 said:

In the event of a hard drive failure...then I would agree.

Well, that's the whole point of RAID1 - in case a hard drive fails. RAID is not for every body. In fact, I don't recommend it for everyone - it is expensive and because it does NOT take the place of a viable backup plan. But if minimizing down time is important to you, RAID1 is the way to go.

RAID is not a suitable replacement for a backup.

I already said, "everyone should have a viable backup plan". Again, RAID1 was developed to minimize loss of productivity due to mechanical failure of the hard drive.

Generally speaking, they don't fail due to mistakes on the parts of admins or viruses/trojans/malware....as is common with a home computer.

That's not looking at it the right way. Hard drives, whether at home or on a corporate network, rarely fail due to malware. The data on the drives may get corrupted, but that is not a mechanical failure. And protection from data corruption is not a function of RAID.

If my server were to fail miserably, the only thing I care about at all is my data. I can reinstall my OS pretty quickly on just about any piece of hardware and just put my data back and I am back in business.

And that's great. But for some people, not only is the data critical, but so is ensuring immediate access to it. They can't afford the downtime it takes for repairs or to assemble a new computer. For not corporate users (that is, they don't have a "volume license agreement with Microsoft), installing the OS on a different computer requires a new Windows license - unless it is a retail license! But most users have OEMs versions that came with their old hardware and which, if you read your EULAs, are NOT transferable to a different computer - PERIOD! Re-imaging is great, but if the hardware is different, you still have to deal with drivers. Nothing insurmountable, but all time consuming. And I would venture to say for many, many people, using a #2 Phillips screwdriver, and moving a data cable and a power cable is LOT easier than rebuilding Windows and restoring data from a backup - AND using the screwdriver and moving cables.

In my opinion, I would focus far more on having a backup plan for your data

I agree. For most users, that is best. And for RAID users, it is still a necessity.

And with regards to having to reinstall the OS....if it's just the hard drive failing...you can just reload and reactive the copy of your OS. You don't need a new license...since the computer didn't change.

I agree with that too and only mentioned the license issue when you said you could install the OS on just about any piece of hardware - suggesting even another computer. If simply swapping drives, you may have to re-authenticate, but you don't need a new license.

My question was half about hardware raid (to be more specific raid 1).

The other half was about Windows 7's mirroring ability. I'd like to learn more about it.

For example
Can I have more than one mirrors?
What happens when the main drive dies? Can I make the mirror "main"?

Hi there
There are better people than me who can advise on Raid vs Mirror.

I just want to add a remark in case people are not aware of it that RAID is NOT a system designed to recover data in the advent of system failure which can be caused either by a hardware failure, a software glitch / virus etc or simple human error -- deleting critical files etc.

In "Simple terms" RAID essentially makes a bunch of disks appear as "a unit" so a failure of any one of the disks within the array *can* and probably will lead to data loss. A decently configured RAID system will improve perfomance A LOT but at a slight risk of potential data lost if a disk goes bad.


This fact is often misunderstood.

Mirroring on the other hand will protect data as after transaction "commit" the data on the first bank will be "copied" or "mirrored" to the second bank of disks.

This has some performance implications - but is used when you need 100% data reliability -- such as Stock exchange "Real time" transactions or some banking applications.

So "You pays your money and takes your choice".

IMO unless you are running a server 24 hours a day and have external customers I wouldn't bother with either on a home network as decent disks on a home computer will still give you really good perfomance.

Bad / slow disks on ANY system whether used in a RAID array or not will KILL performance stone dead -- and I've found over the years it's cheap slow disks that are usually the source of poor performance - except in those cases where there obviously isn't enough RAM in the system -- not normally a problem with todays gear.

Cheers
jimbo

Raid vs Mirror.

Mirror is a RAID type, RAID1 specifically.

Can I have more than one mirrors?

Still don't know what you mean by that. As I said, you can have as many as you have spare disks.

If you mean can you have 4 drives running at once, all mirrors of each other, then no, not on the same computer. You can have a mirror on one computer, then have a mirrored computer elsewhere on network, or across the planet.

In "Simple terms" RAID essentially makes a bunch of disks appear as "a unit" so a failure of any one of the disks within the array *can* and probably will lead to data loss.

No, that is not true. With a striped array, RAID0 for example, then the data is spread across multiple drives, so then if one drive fails, you have lost data. But the whole point of mirrored arrays is precisely for when one of the disks in the array fails, and in that event, there will be NO data loss. Saying it *can* is a bit of a cop out - you *can* win the lottery tomorrow too. But saying it probably will lead to data loss is simply wrong for any mirrored array, and there are several types, not just RAID1, that support Mirroring.