Is Software RAID 5 Worthwhile?

Amd Phenom ii x4 945 / 3 ghz processor
May 22, 2013 at 19:08:12
Specs: Windows XP Pro, Athlon dual core/1GB
Hi

I posted a question a few years ago about whether software RAID 5 was worthwhile - improved security and performance. I got a no on the latter for software RAID 5 and a recommendation that only a dedicated RAID card was worthwhile. I was wondering if this is still the case. I have to build some high performance PCs for financial applications.

Thanks

Pavesa


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#1
May 22, 2013 at 19:36:43
Software is an inexpensive way to implement RAID. But for serious use you want a real RAID card.

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#2
May 22, 2013 at 19:45:57
Hi

thanks for the view, that was the view before. I guess it either works or doesn't on reliability so I guess they must work in that respect, so that leaves speed. The software RAID puts overhead on the processor I guess, so that means a loss of processing power, but presumably it improves disk access speeds, just not (or not nearly?) as much as a dedicated card?

Thanks

Andrew


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#3
May 22, 2013 at 20:57:04
Is RAID necessary? Why not get an SSD for the OS a few choice apps & a standard HDD for data storage?

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#4
May 23, 2013 at 04:01:37
I think you are misunderstand the purpose of RAID. RAID was never meant to improve performance or security.

The purpose of RAID is to provide redundancy and nothing else. That's is what the R stands for. That means that in the event of a disk failure, there was a fall back option with no down time in applications where a few minutes could be disastrous.

If it is performance and security you need you should be looking elsewhere.

Stuart


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#5
May 23, 2013 at 06:50:32
RAID (excepting RAID 0) is a big deal on a busy server because it allows access to your data even in the event of a drive failure. Even a short period of down time can be highly disruptive to normal business activities and very expensive. With hot swap the drive can be replaced with no downtime at all.

But no form of RAID ever devised can do away with the need for maintaining backups. The problem is that RAID only offers protection from drive failure, and even that cannot be relied on. It provides no protection whatsoever from other causes of data loss. For that reason you always need to maintain adequate backups.

RAID is often implemented on a desktop for the wrong reasons, in the belief that it performs better or is some kind of automatic backup. The performance gains, if any, will be minimal. The idea of an automatic backup is attractive, until somebody deletes a critical file and you find that the backup isn't really a backup at all.

RAID isn't a bad idea if used for the right reasons. But if you decide to use it do it right, in hardware.


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#6
May 23, 2013 at 12:59:09
Hi

thanks for all the feedback, very helpful.

Just to clarify a couple of things:

1) when I say security, I mean that a dead drive can be replaced without loss of data and I don't mean as a substitute for a good backup strategy. The idea's often run out though that a backup strategy is a panacea against computer failure but on the failures I've had and not lost data, I've still lost days in setting everything up again and customizing things how I want them and even then you invariably find something that wasn't backed up. Avoiding this altogether with a RAID, assuming it's just hard drive failure, would be a real boon.

2) As I understand it, another benefit of RAID (0) is that striping enables parallel extraction of data from two hard-drives, speeding up extraction of data from computer's slowest core component, hence my reference to improved performance.

With regard to all this, I was interested in riider's suggestion of using an SSD for the OS and choice apps.

I read an interesting article called 10 Surprising Facts About RAID - google it.. saying software RAID is better than hardware because hardware RAID is expensive and if the RAID card fails the RAID volume fails and you need to find an exact replacement card to recover the data, whereas software raid is portable to another machine. Also, SATA 3G & 6G enable hot-swapping of drives and software RAID consumes little processor - claims just 2%-4% on one core in a multicore machine - ie/ irrelevant. He says software RAID works with SSD caching and software RAID supports variable size volumes that you can extend by just adding more disks

I'm interested in thoughts on this.

Thanks

Pavesa


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#7
May 23, 2013 at 13:45:57
another benefit of RAID (0) is that striping enables parallel extraction of data from two hard-drives, speeding up extraction of data from computer's slowest core componen

That's the theory but in practice it doesn't work likes that. RAID 0 will only a show a benefit if you are regularly reading and writing huge files in the Gb range like video files. With normal files in the Mb range and often a lot less there is no improvement and in some circumstance can even be slower as the overhead in controlling two drives will negate any speed advantage.

RAID 0 is not deserving of the tile RAID as there is no redundancy. If a disk in a RAID 0 array fails your data is gone with little hope of recovery. Backups are essential. Most other RAID configurations will be slower as data has to be written twice.

AS LMillar says, RAID is often implemented for all the wrong reasons. Unless you are running a mission critical system, RAID is an unnecessary complication. Especially when you consider that modern drives are a lot faster and far more reliable than they were when RAID was first designed.

Stuart


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#8
May 23, 2013 at 16:28:27
Hi Stuart

thanks for the feedback and thoughts on this, I think you have it spot on right

Seems software RAID still isn't worthwhile unless you are working within certain specific parameters (large video files or databases maybe)

Pavesa


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#9
May 23, 2013 at 17:19:13
Database applications Don't do large file transfers, regardless of how big the database is. They do do a lots of small ones and it is one of the instances where RAID 0 will be counter productive.

Unless you are running a mission critical system, RAID is an unnecessary complication. That applies to both software and hardware RAID. RAID 0 you can forget about altogether.

Stuart


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#10
May 23, 2013 at 17:58:00
Note: I have found from experience that putting your operating system and programs on one partition or disk (or SSD) and putting all data on a separate partition or disk, then keeping an extra hard drive with an image of your OS partition, makes restoring your system/drive much faster and easier. Since the OS and Programs and settings associated with them rarely change much, restoring the image make sense and other files are easily restored from normal back ups.
Combine a SSD SATA3 (6GB/s) with a large fast SATA3 hard drive(s) (WD Black) as needed and another drive to store image and back ups, you have speed, capacity, and protection. For more protection, add off site back up and a portable drive with a duplicate drive image, and you are all set.

You have to be a little bit crazy to keep you from going insane.


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#11
May 23, 2013 at 18:22:42
Hi

thanks so much for the advice, I really appreciate your thoughts on this

Pavesa


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