Mirroring vs Raid

[White Cat]

My Windows 7 is currently installed on a raid 1 array. I am considering on switching from hardware raid to windows 7's mirroring function as hardware raid tends to be problematic if the motherboard dies or is replaced. I am however curious on a number of issues.

First of all, is this a good idea at all. Will I suffer a very serious performance loss? Minor losses aren't that big of a deal but I don't want to regret this. Is windows 7 mirroring a "true" mirroring?

Are both disks bootable? Consider the main disk dying. In RAID 1 I can simply boot without doing anything (aside from pulling out the dead drive). If my main drive dies will the mirror be bootable?

How good is it in terms of avoiding data corruption or loss?

Does windows 7 mirroring provide a performance gain (during read)? It could be twice as fast as there are two disks to read from...

I am planning on making this switch without reinstalling windows. I basically plan on pulling one of the raid disks off the array, format it. Boot from the other disk in raid... Use windows 7 mirroring to make a carbon copy. Remove the remaining disk in raid. Boot from the mirror. And finally use windows mirroring function on the original raid'ed drive.

 

[Jonathan_King]

Hello,

The Windows mirroring will work fine. Both disks should be bootable, and you should not see much performance loss at all.

It is reliable, so no need to worry about that.

Hope this helps,
~Jonathan

 

[Digerati]

I agree, with a couple caveats.

Does windows 7 mirroring provide a performance gain (during read)? It could be twice as fast as there are two disks to read from...

Depends on the system, but generally, yes, there is a little gain, but it is not twice as fast. The seek times are not increased, only the actual reads. There might be a very slight hit in writes - however, but that is not normally something folks see.

Both disks will be bootable, but ONLY IF the reason to break the RAID and boot from one or the other is due to disk failure. In a RAID, if corruption is due to malware or something other than physical failure of a single disk, then neither disk may boot as the corrupted or infected file would be mirrored on both drives. So there is still a need for current backups.

 

[Frostmourne]

Motherboard's do not have hardware RAID, they use the CPU - if you want real RAID buy a proper ($$$) card. As for data loss, store one backup offsite and the other somewhere else, such as a NAS box.

 

[White Cat]

Migrating windows 7

So basically using this I can migrate my windows installation from a hardware raid (real or not ) to a software raid (windows 7 mirroring) without problems. Right?

 

[Jonathan_King]

If you can boot into Windows, you can set up a mirror. It doesn't matter what your other RAID configurations are like.

 

[Digerati]

Motherboard's do not have hardware RAID

WHOA! WHOA! WHOA!!!! That is way incorrect. MANY MANY motherboards have integrated RAID controllers on board! And have for years! You are correct when you say they use the CPU, but an on-board RAID controller is still a hardware RAID. Your statement would be the same as saying on-board graphics, on-board sound, or on-board LAN are not hardware! They most certainly are hardware. But just like a graphics card vs. on-board graphics, a RAID controller "card" is much more capable than an on-board controller, not just because they tend to have more capable components, but because they relieve many of the duties from, and free up other motherboard resources (namely the CPU, RAM, and bus).

So now that we have established that many motherboards do indeed have on-board hardware-based RAID controllers, let's look at the differences here.

First, there are software based RAID systems that basically take two drives (or two partitions on one drive) on standard IDE or SATA interfaces (not RAID interfaces) and treat them as 1 RAID device via a software "program" running in the background. This topic is not about them, and I would not recommend a software based RAID to anyone.

Then there are on-board controllers as found on most new motherboards today. These are hardware devices, however, they typically offer fewer RAID options, and they do use more system resources. But, they are still very effective and capable devices, more than suitable for most users, even hard-core enthusiasts (though they probably would never admit it!).

Then there are add-on cards. These also use some system resources (drivers have to be installed, just like any other hardware device) and the OS must be configured to use it. But RAID controllers cards, just like graphics cards, tend to include a separate more powerful and dedicated processor, dedicated memory, controllers and other associated components, and the necessary drive connections. These are primarily for file servers or where a robust redundancy is "mission critical". Cards are also essential for hard-core gamers with deep pockets seeking bragging rights (and nothing wrong with that).

The biggest advantage to cards over on-board RAID, IMO, is portability. With on-board RAID, if the motherboard fails for any reason, you lost your RAID. But with a card, you can move the card and connected RAID "array" to a different computer and be on your way.

 

[pparks1]

I'm not a big proponent for using RAID 1 (mirrors) at home. I think RAID1 is great in a work environment where you have a server which services hundreds of users and would cause massive disruptions if it were offline. The use of RAID1 here just allows your OS to keep running in the event of a hard drive failure.

At home however, I think it's far better to ensure that you have data backed up frequently to an external drive which you can keep offsite. Generally speaking, people accidentally delete files, or get viruses which wipe out data. And a RAID1 cannot save you from this...as it's immediately deleted from both sides at the exact same time. 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.

 

[Digerati]

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.

 

[pbcopter]

With on-board RAID, if the motherboard fails for any reason, you lost your RAID. But with a card, you can move the card and connected RAID "array" to a different computer and be on your way.

I have used motherboards with Intel IHCxR controllers and was able, very easily, to move to another board with the same or later Intel controller with no data loss. Obviously the operating system needed to be repaired/reinstalled if new board was different but RAID was recognized and all data was intact.

Moved from ASUS P4P800 E Deluxe (ICH5R) to Gigabyte GA P45 UD3P (ICH10R).

 

[Digerati]

Good point. Too bad all boards use compatible controllers.

 

[White Cat]

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.

-----------------------

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?

 

[pparks1]

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.

In the event of a hard drive failure...then I would agree. I think far too often people at home have issues because they screw something up, delete a file or get a virus/spyware/malware/trojan/etc and a RAID 1 mirror doesn't do anything to help with this (unless as you mention below you are rotating out copies on a regular basis).

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.

RAID is not a suitable replacement for a backup. RAID 1 simply provides redundancy. Like I said, with a RAID 1 mirror...if you get a virus or otherwise delete a file...it's gone in both places instantly. RAID technologies should never be used in place of a backup. If people feel their data is so valuable, it's absolutely imperative to back it up, and hopefully placed in an offsite location in the event or a burglary or a fire.

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.

Yes, I am a server admin for a living. I replace failed drives in RAID arrays all of the time. And with work servers, they are managed and controlled by skilled admins. 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 why I see the value of using RAID at work...but not as much at home.

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.

That is not a bad way to go if you are using RAID1.

For me, I keep a dedicated file server box at home that stores anything critical. There is nothing of any real value on my workstations. On my server box, I have 2 hard drives installed for data and they replicate to each other every 4 hours (this way if I do make a mistake and I catch it in time, i can simply restore it from my second drive before my synchronization happens). Then, I have a pair of external drives and approx once per week, I synchronize the data to each external hard drive and I store one of the drives off site. I use robocopy with the /MIR switch to do my synchronizations...so since it only handles files which have changed or are removed...my sync jobs usually take less than 2 minutes to perform.

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. There is nothing unique or challenging on my dedicated file server box as I don't use it for anything else. Thus, it's a plain vanilla install and OS patches.

 

[Digerati]

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.

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.

 

[pparks1]

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.

I understand. But my point was that I feel that most home users actually suffer more from accidents, viruses and malware than hard drive failures. Thus in these cases, a RAID implementation would not have helped. But it will increase costs, complexity, etc.

Like you said, RAID setups are not for everyone and my personally belief is that they often aren't a great solution for home use. In my opinion, I would focus far more on having a backup plan for your data as I feel that this will come into play more than being safe from a hard drive failure. So, please don't take my posts as an indicator that you are wrong in any way...this is just my viewpoint and a different way of thinking.

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.

 

[Digerati]

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.

 

[pparks1]

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.

Sorry, I could have been more clear as well. With the way that I do my backups, it's just a file copy using robocopy to an external drive which is formatted NTFS.

When I mentioned that I could use just about any piece of hardware, I could also install Linux on another machine and mount those drives and have access to my data with no cost for licensing. Of course, this option is likely outside of the skill set of the average computer user as well.

 

[White Cat]

My question...

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"?

 

[jimbo45]

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

 

[Digerati]

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.