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RAID1 disadvantages?

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  • Hard Drives
  • NAS / RAID
  • Performance
  • Storage
Last response: in Storage
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November 24, 2009 7:09:15 PM

Hi,

I am in the process of building a new PC and since my data is important. I am considering using RAID. I currently have an external HD which is being backed up using Norton Ghost, but I would feel much more comfortable with real-time protection I've read that with on-board RAID controllers, the performance hit for RAID 5 is enormous, so I'm leaning towards RAID 1. I will be using WD 750 Gb Black hard discs on a GIGABYTE GA-P55A-UD4P motherboard using Windows 7. Is the only disadvantage to RAID 1, the 'loss' of a hard disc and a slightly more complicated O/S install with the advantages of data protection and a potentially slightly better read performance?

Thanks so much...

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November 24, 2009 7:28:20 PM

You pretty much have it.

By the "loss" of a hard disc I assume you mean using one more. To this you need to add increased failure rate from two drives and slightly increased power consumption. Also a small hit to system resources that will marginally slow performance, probably not noticeable in most cases and not enough to sway a decision. I only mention it since it apppears you are trying to be thorough.

Have you considered what data you need to backup and what you don't? I find I have very little data - only several GBs - that I really need to backup. Things like music and videos for which I have the original CD I don't need to back up. I used to back free downloaded apps - but then I found I usually went looking online for the updated versions anyway - so I no longer back them up. You can paritition both HDs and use one set of partitions in RAID 1 for you data, that have the leftover on each drive as separate, non raid drives for music, purchased, videos, backing up drive with OS, and what not.

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a c 415 G Storage
November 24, 2009 9:52:13 PM

RAID 1 doesn't really protect your data - that's what your backups are for. What RAID 1 does is eliminate downtime due to disk failure. That's the sense in which you should evaluate whether it's worth it for you.

If you can tolerate the downtime required to replace the failed drive and restore the data from a backup, then there's a good chance you don't need RAID 1.
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November 24, 2009 10:02:06 PM

sminlal said:
RAID 1 doesn't really protect your data - that's what your backups are for. What RAID 1 does is eliminate downtime due to disk failure. That's the sense in which you should evaluate whether it's worth it for you.

If you can tolerate the downtime required to replace the failed drive and restore the data from a backup, then there's a good chance you don't need RAID 1.


I agree, but throughout my IT career most loss of data has come from HD failure. I want to protect myself against:
- Any loss of data (I have tons of personal documents and photos as well as my wife's design business on my hard disc)
- The annoyance of having to re-install the OS and all software in case of a failure

Yes, I am still vulnerable to viruses, theft or other disasters but my major concerns is disc failure. I will store my external hard disc at another location and will make external backups once a month to cover for all other occurrences that will require a backup...

Storage is so ridiculously cheap these days that RAID1 is almost a no-brainer in my humble opinion..
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November 24, 2009 11:06:31 PM

I agree with you exm
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a b G Storage
November 24, 2009 11:11:33 PM

sminlal said:
RAID 1 doesn't really protect your data - that's what your backups are for. What RAID 1 does is eliminate downtime due to disk failure. That's the sense in which you should evaluate whether it's worth it for you.

If you can tolerate the downtime required to replace the failed drive and restore the data from a backup, then there's a good chance you don't need RAID 1.

I'd say that it does protect your data, but used alone (without a good backup), it only protects it from disk failure. For full protection, you still need a good backup.
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a c 415 G Storage
November 25, 2009 4:37:06 AM

What I mean when I say "RAID 1 doesn't protect your data" is that it doesn't protect your data from all risks. An offsite backup DOES protect your data from all risks worth considering, so if your data is important that's what you REALLY need.

Assuming you have the backup, the only additional thing that RAID 1 does for you is faster recovery (ie, you don't have to re-install everything, restore from backup, and redo the work you did since the last backup). Therefore, IMHO that's the benefit that RAID 1 gives you and that's the way you should evaluate whether it's worth it or not.

I'm certainly not trying to tell anyone that RAID 1 is not worth it - that depends on each person. But when you're making the decision whether to use it or not it's important to understand just what RAID 1 does and doesn't do for you.
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November 25, 2009 11:46:04 AM

sminlal said:
What I mean when I say "RAID 1 doesn't protect your data" is that it doesn't protect your data from all risks. An offsite backup DOES protect your data from all risks worth considering, so if your data is important that's what you REALLY need.

Assuming you have the backup, the only additional thing that RAID 1 does for you is faster recovery (ie, you don't have to re-install everything, restore from backup, and redo the work you did since the last backup). Therefore, IMHO that's the benefit that RAID 1 gives you and that's the way you should evaluate whether it's worth it or not.

I'm certainly not trying to tell anyone that RAID 1 is not worth it - that depends on each person. But when you're making the decision whether to use it or not it's important to understand just what RAID 1 does and doesn't do for you.


Interesting topic... I am not disputing the need for an offline backup, but any backup has the following disadvantages:
- Is the backup reliable (how many people actually test their backups)?
- Do you lose any data (if you backup once a week you potentially can lose 6 days of data)?
- Is the backup running (we're all human and we're not running professional servers, so it's normal to 'forget' to run or enable backups)

So I still think that the combination of RAID1(5/6/10) and an offline backup provides maximum security. And as I said above, with the prices of storage there's really no reason not to use RAID1...
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a c 367 G Storage
November 25, 2009 3:31:37 PM

You seem to have a good handle on this, and lots of good comments from others here. I'll add a few.

The big advantage or RAID1 is "instant recovery" from HDD failure. That is, if a member of the array fails, the RAID system immediately should detect that situation and convert the operation to using only the remaining good drive so that you can keep on functioning normally right away. It should also immediately send out a warning message so that you know of the problem and can plan its repair as soon as possible. The "downside" of this is that it can work so smoothly that the warning message goes un-noticed or is ignored by untrained users and the tech guys are unaware a problem needs attention. That's probably not your situation.

The RAID1 systems I have used have very good tools for fixing a drive failure. Basically they will pinpoint exactly which drive is faulty so you can replace it. Then they will allow you to control re-establishing the array by copying everything from the good drive to the replacement unit. There is no need to re-install an OS or restore data from a backup dataset. They even can do this while the system is in use, although my preference would be to do the re-establishment as a separate operation on a system that is NOT being used for anything at the time.

My wife runs a retail store with a POS software package on a dedicated computer. The data files for that operation are kept in one subdirectory and amount to about 60 to 70 MB of data that are updated with every sale. The files are generally in ASCII character strings with some numerical data, so they compress well to .zip files. I set up the machine with a pair of drives in RAID1 as the only drive system. I installed WnZip Pro and set up a scheduled task that runs every day at 10 minutes before midnight (store is closed). It zips all the files in the specific subdirectory into a daily .zip file named with a date string and puts them in a designated subdirectory. This guards against data file corruption by providing end-of-day archived versions. Once a month (probably should be more often) I simply copy the end-of-month .zip file to a USB drive and take it home where I put it on my home computer - thus an off-site backup monthly. Then I delete all the daily .zips at the store, except for that month-end one. (So the store computer has on its RAID1 array an end-of-month .zip file (for every month since its start), each containing a snapshot of all the data that changes over time.) Small important step: the POS computer normally runs 24/7, so when I do the monthly .zip file copy I also reboot the machine and watch the POST messages to be sure there are no errors in the RAID system that I have not heard about.

We had a failure, but not of a hard drive. The mobo failed and had to be replaced. That can be a big problem with any RAID array based on mobo built-in "controllers" because there is no real universal RAID standard. That means often a RAID array written in one system cannot be read by another. In choosing the original mobo (by Abit) I deliberately chose one that had an nVidia chipset because their website claimed that they guarantee that ALL of their mobo chipset RAID systems use the same RAID algorithms and would continue to do so, so that any yet-to-come nVidia chipset could handle any older RAID disks made with their chips. When the mobo failed I selected a Gigabyte replacement mobo with a similar (but not identical) nVidia mobo chipset. Swapped everything, plugged it all together, and booted expecting maybe I'd have to do a Repair Install at least. It just booted and ran perfectly first time - no trouble at all! WOOHOO! I never had to reconfigure or re-install anything, other than updating the mobo device drivers from the Gigabyte CD.

So if you plan for possible changes to the RAID controller system as well as for changes to a hard drive that fails, a RAID1 system can give you some data security and continued operation through disk failure. You just have to recognize the need for real data backups and do them (AND VERIFY, as you say), probably more often than I do it.
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November 25, 2009 4:07:07 PM

Paperdoc: excellent write-up and I agree with your approach. What you might consider for the .zip file backup is an online backup solution. Those are relatively inexpensive and you can automate this on a daily base. Just a suggestion.

Regarding Raid1 failure: I've read that in theory you can take a drive out of a Raid1 array and plug it in another computer without any problems (something you can't do with any other, striping, RAID solutions). This would mean that if you're motherboard fails, you should not have any issues with replacing the motherboard with another model. However, you might be able to access the data on another motherboard, but you will lose the RAID1 array that you need to rebuild.

As I said in my OP, originally I was planning on a Raid 5 array but the performance penalty for a software based array (and being 'stuck' with one motherboard type) made me decide to go with Raid1. I don't believe that striping (Raid 10) benefits to such an extend to warrant additional hard discs, to introduce more points of failure (more hard discs) and having to use the same brand of motherboards.

I purchase the Western Digital Black 750 Gb hard discs for $65 each a few weeks back on Newegg, so the $65 is worth the benefits of Raid 1 to me. And it seems reading all of this that Raid1 is not the holy 'backup' grail, but there are no negatives either (besides the $65 investment).

Thanks to all and if you want to keep this topic going, feel free to discuss. It's great to hear other people's opinions.
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a c 367 G Storage
November 25, 2009 6:10:30 PM

The stories of being able to move one disk from a RAID1 array to another machine and use it as if it were a normal independent drive may or may not work. In some cases I've read, the new machine chokes on it. It appears that some RAID1 systems write to their disks' Partitiion Table / MBR some data that some other systems (RAID1 or not) cannot understand properly, and so they simply give up and send out scary messages like there is no disk or it needs to be Formatted. However, the truth is simply the Partition data contains a couple of unexpected values. Certainly in that situation a Partition Recovery and Data Recovery utility can get it all back because the actual data are just fine. But that's such a big hassle!

On the other hand, given that some systems will allow you to migrate the TWO disks in a RAID1 array to another machine with a similar RAID1 controller (as in my case), I certainly would expect that those cases ALSO would work for moving only one of the disks. After all, in this hypothetical case the new machine will "see" one good member of a RAID1 array it fully understands, and one faulty or missing HDD unit paired with it. It should handle that just as if it had encountered a previously-functioning RAID1 array that suddenly is missing one of its members.
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a c 415 G Storage
November 25, 2009 7:52:26 PM

Excellent comments, Paperdoc!

I can't stress enough the importance of testing your recovery procedures if you plan on using RAID for redundancy. The last thing you want is to unplug the wrong drive from your RAID controller or type "Y" when you should have typed "N" and end up with all of your data unrecoverable. When you set up a RAID system you really, really need to do a trial run of how to recover from a drive failure before you commit production data to the array. And if you're smart you'll take some screenshots (use a digital camera if necessary) and squirrel them away somewhere along with some notes so that you can recover with confidence when the time comes.

Pay particular attention to how you identify which drive is which. A lot of motherboard RAID users have no idea which drive corresponds to which SATA port which corresponds to which volume as known by the RAID software. If all else fails, one way to avoid confusion is to use drives from different manufacturers so that if the RAID system reports that the "Seagate" drive failed it's really, really obvious which one to remove.

IMHO, unless you've been able to test a recovery procedure ahead of time, you should plan on treating a motherboard or RAID card failure as a disaster that requires recovery from your backups. If you find some sneaky way of getting the data back without resorting to that, then good for you. But you need a disaster recovery plan too. No RAID system in the world is going to help you when you walk in to find that the computer has been stolen...
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February 15, 2010 4:22:30 AM

really a good post for a beginner who want to buy a raid ex HD case .
Thanks all of you !!

About the "no universal raid standard " , I would like to know more about it .
As I am going to buy a iomega external HD case which have two bay for raid 1 ,
I would like to ask is that mean when the case failed , but not the HD , then I cannot just plug the HD to my main board and read the data ?
That would be very horrible for a newbie to buy it as I think the chance of failure for a HD case should be similar to a HD drive .
I am not a IT guy but my experience was that most the computer disaster of mine were all caused by disk failure/data lost so I must push my self to a raid file system . I dont put any file in my C drive for a long long time .
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February 15, 2010 12:54:46 PM

DreamTree said:
really a good post for a beginner who want to buy a raid ex HD case .
Thanks all of you !!

About the "no universal raid standard " , I would like to know more about it .
As I am going to buy a iomega external HD case which have two bay for raid 1 ,
I would like to ask is that mean when the case failed , but not the HD , then I cannot just plug the HD to my main board and read the data ?
That would be very horrible for a newbie to buy it as I think the chance of failure for a HD case should be similar to a HD drive .
I am not a IT guy but my experience was that most the computer disaster of mine were all caused by disk failure/data lost so I must push my self to a raid file system . I dont put any file in my C drive for a long long time .


If you use RAID1 you're fine. "Worse" case is that you have to restart the RAID array, but you won't lose any data. RAID0 or RAID5 could be more problematic.
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a c 367 G Storage
February 16, 2010 2:09:43 PM

DreamTree, what you suggest may work, or may not. Or maybe, you can make it work with little effort.

The root of the question is in the details of HOW the RAID system in that external Iomega case writes its data to the drives. Any drive system must, as the very first step, write to a HDD unit two key things known as the MBR and Partition Table. All BIOS systems look on a HDD for those pieces of info in a fixed place at the start of the drive. THE MBR basically is a small bit of code that can read the very first data from the drive. It really is a loader for a larger machine-language routine that actually does load and read the rest of the disk, according to the OS installed. The Partition Table contains details of exactly how the available space on this HDD hardware unit is allocated (in contiguous blocks) to Partitions that each will be treated as one logical "drive". Now, some RAID systems write these in such a way that any other common OS like Windows can read those two and understand them enough to start the loading process and get a basic boot into the OS going. Some, however, write slightly different data in places and Windows cannot use them to boot from.

In almost all RAID1 systems there is a way to un-RAID the drives. Now, on the drives ALMOST everything is identical between the two units, except for a few small details in those MBR and Partition Table records. The simplest way that a RAID1 system can "Break" an array into stand-alone individual drives is to re-write those few items in a way that Windows or any other OS can understand. Thus BOTH drives become perfectly good usable drives - they just happen to be complete copies of each other. And hence, they can be used anywhere with all their data. HOWEVER, if that operation to "Break" the RAID1 array is NOT done first and you take one HDD unit and try to use it as a stand-alone unit, that may not work, depending on the details of how that particular RAID1 system writes its info at the beginning of each of its member units. So, it night work, and it might not.

There is another way this can be done in most cases. We are talking about what happens when the Iomega 2-disk RAID1 enclosure fails because some part of the enclosure (e.g., the RAID controller, or the power supply, etc.) failed but left the disks unharmed with good data. By far the simplest first step would be to go to Iomega and ask them to supply either a replacement identical drive case, or a newer unit that uses the SAME RIAD1 algorithms and hence can read those drives with no trouble. With a long-standing company like Iomega I would expect them to be able to do this. BUT I suggest you inquire carefully about that possibility BEFORE you decide which external RAID box to buy. And, of course, you should also ask whether that would be completely unnecessary. IF their way of running the RAID1 array is such that you actually CAN simply take one drive unit out of the case, plug it into a computer as a normal stand-alone drive and use it right away with NO special step to "Break" the array first, then you will not have a problem.
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February 25, 2012 5:48:26 PM

sminlal said:
Excellent comments, Paperdoc!

I can't stress enough the importance of testing your recovery procedures if you plan on using RAID for redundancy. The last thing you want is to unplug the wrong drive from your RAID controller or type "Y" when you should have typed "N" and end up with all of your data unrecoverable. When you set up a RAID system you really, really need to do a trial run of how to recover from a drive failure before you commit production data to the array. And if you're smart you'll take some screenshots (use a digital camera if necessary) and squirrel them away somewhere along with some notes so that you can recover with confidence when the time comes.

Pay particular attention to how you identify which drive is which. A lot of motherboard RAID users have no idea which drive corresponds to which SATA port which corresponds to which volume as known by the RAID software. If all else fails, one way to avoid confusion is to use drives from different manufacturers so that if the RAID system reports that the "Seagate" drive failed it's really, really obvious which one to remove.

IMHO, unless you've been able to test a recovery procedure ahead of time, you should plan on treating a motherboard or RAID card failure as a disaster that requires recovery from your backups. If you find some sneaky way of getting the data back without resorting to that, then good for you. But you need a disaster recovery plan too. No RAID system in the world is going to help you when you walk in to find that the computer has been stolen...


Like your last statement, Sminlal--RAID 1 + Backups should be treated separately.
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