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Windows 7: What happens to the data on a mirrored volume when one drive goes bad?


12 Dec 2011   #1

Windows 7 Home Premium, 64-bit
 
 
What happens to the data on a mirrored volume when one drive goes bad?

For backup purposes, I want to take two 1 TB hard drives, make them dynamic disks, then mirror them using the disk manager in Windows 7. After I do this, of course, it looks like one drive to the OS, not two. So I'm writing my data to them, storing music and movies and whatever on them so now there is an identical copy of the data on both drives. Now what if one drive fails or I just yank one drive out of the machine. When I reboot the computer, will Windows just see the one drive that's still working, and just make the data available on it like nothing ever happened? Perhaps I would simply need to convert the disk back into a "normal disk" with Disk Manager?


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12 Dec 2011   #2

Microsoft Community Contributor Award Recipient

Windows 7 SP1, Home Premium, 64-bit
 
 

Offhand, I wonder why you are using such a method.

You may have a good reason, I don't know.

Normal practice would be to write to drive A and then separately back A up to B, without dynamic disks.

If I understand you correctly, you are writing to A and B simultaneously?

What's the advantage to that?
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12 Dec 2011   #3

Windows 7 Home Premium, 64-bit
 
 

The advantage, sir, is simplicity! Image how simple backing up a drive will be, when every piece of data I write to one drive, is automatically written to the other. That means I don't have to mess around with making backups, remembering to make backups, checking backups for data integrity, not having to mount previous backups as a drive to explore them (such as in Acronis and others) and everything. In fact everything I put on one drive will instantaneously be backed up to the other drive so that I don't have to wait for my once-a-week backup to start. I also wouldn't need to spend money to buy backup programs, or learn to use them, or even mess around with it at all, except for when I make an image backup of my boot partition. See the simplicity? In Windows Explorer I will only see two drives: my main boot drive (An SSD, which I will backup separately) and my storage drive (which is actually 2, maybe 3 drives, mirrored). Piece of cake. What happens though, when one of those storage drives fail? Is the data corrupted on the mirrored drives automatically, or does Windows not even really notice that one drive is no longer there, or what?
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12 Dec 2011   #4

Microsoft Community Contributor Award Recipient

Windows 7 SP1, Home Premium, 64-bit
 
 

I don’t know the answer to your question.

Maybe you are doing this for reasons other than backup?

I do know that I would not want to be in a situation where I did not have access to earlier versions of my files.
I would not want to unknowingly make an error in a file, such as a formula in an Excel file, and have that error simultaneously propagated to my “backup”.

If you are specifically referring to RAID O, my understanding is that if data on one disk is lost, then all data in the RAID 0 array is lost. There might be some performance advantages, but it’s a poor choice for critical data.
My System SpecsSystem Spec
12 Dec 2011   #5

Windows 7 Ultimate x64
 
 

You are talking about RAID1,

The benefits are instant backup with no user intervention and faster read times (as data can be read from disks simultaneously).

This comes at the cost of only 1 drive capacity available to use.

Normally you can just yank the bad drive and put the good drive in a new slot (so it's no longer part of the array).

Edit: I don't know why you need to make the disk dynamic?

Edit 2: this only protects against drive failure/corruption. Malware or other filesystem damage caused by instructed writes will still be replicated. So images are advisable.

Edit 3: having 3 drives mirroring seems like a waste to me, in the event of failure the array will detect it and report to you. If you are planning 3 disks for storage I would use one of them for image and 2 mirrored
My System SpecsSystem Spec
13 Dec 2011   #6

Windows 7 Home Premium, 64-bit
 
 

Thank you for shedding some light. I'm interested in making a dynamic disk because I have to in order to make a mirrored volume across two or more HDDs in Windows 7 don't I? That's the only reason really. If there was some microsoft software that simply kept in sync all data from one drive to another, I would probably use that instead.

I realize that a malware infection could destroy all my data since it wouldn't be inside of a compressed and encrypted backup, but I'm feeling okay about this since I never ever get a virus due to very safe surfing habits, getting timely updates from Microsoft, and using good antivirus software.

I'm just wondering what happens when one drive that is mirrored with another (as a mirrored volume created in Disk Manager in Windows 7) suddenly becomes unreadable. Since the same exact data exists on the drive that's still working, would it be readable to Windows even though it is no longer part of that mirrored volume?
My System SpecsSystem Spec
13 Dec 2011   #7

Windows 7 Ultimate x64
 
 

Sorry, just understood, you want to do this in windows disk management and not from a RAID card or on-board RAID support.

Disregard everything I said and go:

Best practices for using dynamic disks on Windows Server 2003-based computers
and
Disk Management
My System SpecsSystem Spec
13 Dec 2011   #8

Windows 7 Ultimate x64 SP1, Windows 8.1 Pro x64
 
 

For a long time I had RAID 1 set up for my data. This worked well and when a disk failed (only happened once) the other continued operating until I could replace the bad drive.

Then, for various reasons that have been fixed, I began to experience system freezes and BSOD's.

Each time this happened, the RAID 1 would begin a verification that would take hours to complete.
No big deal but, in a few cases, the array became corrupt and required Chkdsk to be run before I could access the data. I realized then that if anything causes corruption, both drives in the array will contain the same corruption.
I have since decided to just continue with regular backups, which I have always done anyway, and remove the RAID from my system.

Just my opinion.
My System SpecsSystem Spec
13 Dec 2011   #9

Windows 8 Pro (32-bit)
 
 

Quote   Quote: Originally Posted by Sub Styler View Post
Edit 3: having 3 drives mirroring seems like a waste to me, in the event of failure the array will detect it and report to you. If you are planning 3 disks for storage I would use one of them for image and 2 mirrored
If you have 3 disks then wouldn't it be better to use raid5? you'd still have two devices worth of storage.
My System SpecsSystem Spec
14 Dec 2011   #10

Windows 7 pro 64bit. (SP1)
 
 

Quote   Quote: Originally Posted by ignatzatsonic View Post
Offhand, I wonder why you are using such a method.

You may have a good reason, I don't know.

Normal practice would be to write to drive A and then separately back A up to B, without dynamic disks.

If I understand you correctly, you are writing to A and B simultaneously?

What's the advantage to that?

Its called RAID1 or mirror raid.
Its different from backup in some ways. as you told backup makes copy/image/archive (depends on software) to other drive/network/other media
RAID1 always has mirror copy of the data in real time.
On critical servers RAID1 and backup is used same time
RAID1 protects from mechanical failure (if one disk breaks other disk continues to work)
Backup gives protection from data damage (virus, user delete files etc.)
RAID1 does not protect from data loss, viruses, deleted files etc because when data gets corrupt its mirrored to other drive in real time (Most backup software only backups when sheduled, and may contain several different date/time backups)
But most backup does not protect from drive failure because if your drive fail you need to restore data to previous date (so you lose some data, of course it all depents on what you are doing).

To answer thread starter question
it depends on many things raid controler or software.. there is hardware and software raid.
windows server OS support software raid. but its always better to have dedicated RAID hardware.
Windows server software RAID1 will work if one drive fails it will be able to boot from another. and when you replace failed drive it will rebuild data. (make mirror again)

For home user only backup usually sufficient.
There is also RAID0 (for faster read/write but not for data protection it even decreases data protection from HDD failure) and other RAID versions for example you can mix 1 and 0 for speed and security.. other like 5..
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 What happens to the data on a mirrored volume when one drive goes bad?




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