RAID Explained in Different Configurations/Environments

HTPC

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Jan 12, 2014
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I'm an amateur IT/computer enthusiast so I apologize in advance if people feel these questions have been asked/answered elsewhere. Links to other articles that will help answer my questions would be great - I don't at all mind doing the legwork.

I've read through many forums on this topic but it's still not entirely clear to me when the appropriate time is so use a RAID setup and whether that should be done via hardware (through the MB BIOS (?) or discrete controller) or in software (spanned, stripped, mirrored, etc. in windows for example).

To give you a sense of what I'm trying to do - I'm trying to figure out the optimal way to configure three machines at home. I have a dedicated HTPC, a separate work machine, and a server.

In the HTPC I have a Samsung EVO SSD for W7-Pro and a single 3TB WD red drive (for "DVR" storage).

In the work machine I have an Intel 520 SSD for Win7-Pro and two 2TB WD green drives.

In the server I have an Intel 520 SSD for Win7-Pro, three 3TB WD red drives, and two Toshiba 3TB drives.

I also have a couple of older (SATA II) Intel SSDs and another Intel 520 laying around that could potentially be incorporated into any of these builds.

I'd like to configure the system such that some portion of the storage on the server is fully redundant and I will not lose data in the event of hardware failure. The data stored on these drives would be things like photos, documents, etc. that is not backed up anywhere else (I.e. The server is the only storage location). I would also like to use the server to backup information on the other machines (at least portions of it) but that seems pretty straightforward in terms of redundancy (data would be in two locations).

Some questions are:
1) What would be the best architecture for my setup to accomplish what I'm trying to do?
2) Is there any value in installing windows in a redundant way on the server (two SSD's)?

I would be happy to provide additional information if needed. Thanks!

-E
 
Solution
The problem with mirrored drives is the fact that they are identical copies of the data. So consider these scenarios:

1. A hard disk fails. You replace the failed disk, the mirror rebuilds and all is fine.

2. You accidently delete a file or folder. The delete is instantly replicated to the other drive and the data is lost.

3. Some external event causes file system corruption. That corruption is instantly replicated to the other drive and the data is lost.

My experience is that 2 is a relatively common occurrence, 3 less so, and 1 is fairly rare. On average a disk will fail after maybe 5 years of use. Furthermore, modern disks contain SMART data that will warn you in advance that the disk is likely to fail soon.

So RAID protects...

legokill101

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Apr 10, 2013
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i would recoment raid 1 you work machine since you need 3 for raid 5 and 4 for raid 6 although it will mean you will only have 2tb of storage as oposesded to 4 because it clones the drive for the server i would recoment raid 6 since it provide protection against two drives ie, one failing and then one failing during a rebuild
 
The first thing that you need to understand about RAID is that it is not a replacement for a proper backup strategy. Backups of any important/irreplaceable data must be kept on a separate system (tape, DVD, hard disk - there are many choices). Many people make the mistake of using RAID as their only form of backup.

From many years of experience managing a network of about 1,000 computers, with several file servers, I can tell you that the commonest reason for data loss is human error - the wrong file is deleted or copied over. RAID does not help you in this situation one iota. The only real reason to use RAID nowadays is if you cannot afford any downtime; in my work situation, with several hundred people relying upon shared resources on a file server, it was not an option to take time off (during the day) to restore from backups in case of a disk failure. This is where RAID-5 (or simple mirrored disks) have a place.

In a home environment I can't see any real need for RAID. You have to have a backup of your data anyway (once again, RAID is not a backup policy!) and it isn't the end of the world if, in the event of a disk failure, you need to restore from those backups and it will take several hours to do so. So I would say forget about RAID and concentrate instead on your backup system (unless I am mistaken and you need to run your systems 24/7 without appreciable interruption in service). Rather than wasting the disks on RAID make them part of your backup strategy.
 

HTPC

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Jan 12, 2014
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Yeah - the "backup" solution is what I'm interested in understanding more about. In my simplistic world, a "mirrored volume" in windows is two drives that contain the exact same data and hence would be a redundant backup. I've also seen this referred to as "RAID" (albeit software RAID). I understand the speed advantages of utilizing a RAID configuration but don't fully understand how RAID provides fault tolerance (if it does) or how drives can be hot-swapped. Either way, I don't need to do either of these things, I just want to make sure that my critical data is tolerant to drive failure and I'm curious if/how I could be smarter in terms of how the other drives are configured (if RAID has some advantages then perhaps I should utilize it on my server for example, especially if it may provide some protection against drive failure).
 

HTPC

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Jan 12, 2014
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...so I guess a more pointed question would be why a mirrored drive configuration would not be considered a "good" backup solution (or would it).
 
The problem with mirrored drives is the fact that they are identical copies of the data. So consider these scenarios:

1. A hard disk fails. You replace the failed disk, the mirror rebuilds and all is fine.

2. You accidently delete a file or folder. The delete is instantly replicated to the other drive and the data is lost.

3. Some external event causes file system corruption. That corruption is instantly replicated to the other drive and the data is lost.

My experience is that 2 is a relatively common occurrence, 3 less so, and 1 is fairly rare. On average a disk will fail after maybe 5 years of use. Furthermore, modern disks contain SMART data that will warn you in advance that the disk is likely to fail soon.

So RAID protects against the extremely rare (nominally once ever 5 years event) whilst providing no protection against the rather more common causes of data loss. A backup strategy copies data to another medium at regular intervals and doesn't automatically delete data when it is removed from the source. Because it copies at the file level, rather than replicating sectors, it is unaffected by file system corruption of the original data. Normally it retains a number of past versions of data allowing a return to the state on a given date in the past. Time Machine on OS X (similar software exists for PCs) is an excellent example of modern backup software.

So RAID does prevent against the rare event, and allows the computer to continue to work with no downtime, but is expensive on resources to provide that limited protection.
 
Solution

popatim

Titan
Moderator
I closed your duplicate thread on this. Below is the sole response posted in it.