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I have a couple of SATA hard disks RAIDed for safety in my machine, because I'm worried about the drive having some sort of mechanical failure and losing my data. I'm considering switching to an SSD next year when the prices have come done a bit.

Is it worth using a RAID with SSDs? It seems like the major cause of mehanical failure will have been eliminated by using the SSD, so you're basically trading "Chance of SSD failure" for "chance of cheapo motherboard raid controller failure". I'm not sure if that's worth it.

Opinions?

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RAID does not protect you from losing important data. That's not what it was designed for. You need backups for that. –  davr Aug 7 '09 at 23:39
    
What kind of up-time do you need? If you can live with a day or so (an hour if you keep a spare nearby) of down-time when the drive fails, while you get a replacement and restore your backups, then it's not really needed... –  Oskar Duveborn Aug 8 '09 at 0:04
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Why do you think SSDs won't fail? Because there are no moving parts? Electronics can and do fail. –  David Aug 9 '09 at 4:33
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@David: Of course electronics can fail, but SSDs are (I assume) less likely to do so than hard disks, because of the lack of mechanical parts. –  Colen Aug 9 '09 at 22:03
    
@Oskar if the SSD fails you lose all the data on it, and restoring from backups takes time. Recovery isn't as easy to attempt with a SSD than with a HDD. –  Mircea Chirea Aug 23 '10 at 8:17

7 Answers 7

up vote 17 down vote accepted

If you don't mind the cost, then there's nothing stopping you from RAIDing SSDs.

Always go with software RAID if you're not running a server! Software RAID is transferable between machines, and hardware RAID often isn't.

Personally, I wouldn't bother with RAID on the current generation of SSDs. Just get the one, and ensure you have sufficient backups that you don't feel concerned about loss of a drive. With the current price and size of SSDs it will be cheap and easy to back up, and then when they get cheaper and larger in the future (as they invariably will) I'd buy more :)

I'd also suggest looking at the MTBF of SSDs and hard disks, and calculating the chances of a failure (and the types of failure -- they may not be as catastrophic with SSDs, as a single sector breaking may not be a sign that the whole drive is dying as it can be with HDDs) and work out if the SSD has a higher or lower chance of failing than a set of RAIDed hard disks...

Edit : The official server fault blog says that this very site is going with RAID-ed SSDs now : http://blog.serverfault.com/post/our-storage-decision/

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What exactly do you mean by "software raid"? Do you mean the stuff that motherboards do (as opposed to "real" raid cards), or some sort of magic raid that Windows knows how to do? –  Colen Aug 7 '09 at 22:27
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@Colen Some magic that $OS knows how to do. I assume that Windows can manage software RAID, with something in the "Dynamic Disks" with mirroring and such (I know that Linux and plenty of other OSes can but I don't use Windows that much). Fake RAID on motherboards is worthless and often performance is no better (sometimes worse!) than OS-supported software RAID. –  David Gardner Aug 7 '09 at 22:33
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Desktop Windows variants without "home" in their name (2000, XP Pro, Vista, and presumably 7) support RAID0 and RAID1, and server variants support RAID5. Linux supports just about every significant RAID type thing and its dog. Unless you get a proper dedicated hardware-only RAID controller from a good manufacturer, go with software RAID. Cheap hardware+software RAID (as seen on cheap controllers and included in many motherboards) is a convenient mix of the worst both! –  David Spillett Aug 7 '09 at 22:57
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TRIM doesn't work with RAID yet so, no - don't RAID your SSDs until they do... –  Oskar Duveborn Jul 4 '10 at 23:46
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@Legooolas (& @ Oskar): TRIM is not supported by either Windows or Linux software RAID at the moment. There are some experimental scripts that can use hdparm's manual TRIM support for RAID 1 arrangements (like kerneltrap.org/mailarchive/linux-raid/2010/5/25/6885148 for instance) but probably nothing I'd consider stable+tested enough for production use. –  David Spillett Oct 1 '10 at 10:41

SSDs can and do fail. I'd say yes RAID them just to be safe.

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Agreed. Especially with some of the problems that have been cropping up with them recently. –  David Aug 9 '09 at 4:42

If you use software raid you remove your "chance of cheapo motherboard raid controller failure". With today's processor speeds, the CPU time required to do the parity calculations is tiny (and you are likely doing this already in the CPU with most half-baked consumer raid chips). When doing some of my own benchmarks I have actually seen software RAID outperform enterprise RAID cards when in write-through mode (I assume your motherboard does not have a battery backed cache to allow you to operate in write-back mode).

So, unless you have something against software raid, I think you lose very little by going with software raid and gain the increased reliability.

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+1. Being bitten by poorly written desktop-motherboard BIOS fake-RAID has made me shy away from any RAID other than hardware based. –  p.campbell Aug 7 '09 at 22:00
    
@pcampbell, I've had RAID controllers fail, and even the same chipset not recognize the array, after replacing the controller. Software raid is the best solution to this, and on modern systems with many CPU cores, it isn't much overhead. I'd still suggest a SATA/SAS controller for increased I/O throughput, but use software RAID. Unless you are specifically using an environment that needs hardware raid, such as ESXi/VMWare. –  Tracker1 Apr 27 '12 at 18:45

I do not have any direct experience with RAIDing SSDs, but I was talking to a Dell rep last year and asked the same question. He said that the IO time actually increased with the RAID, and he didn't suggest it.

I thought about this for a while. For the most part you want the RAID for just a few reasons: speed, redunancy, and/or space.

On the speed issue, there are no moving parts. On a normal drive moving the head and waiting for the disk to spin around to the correct spot probably takes most of the access time. SSDs just don't have those parts, so it should not be an issue.

On the space issue, a logical volume can handle that and no real need for RAID.

On the redandancy, I don't know. It would be an interesting test to see if you received any benefits. I believe the SSDs have "extra" space in them, so when "blocks" go bad there is a spot to put the data. I have only looked at that section in the most casual manner.

Hope I helped,

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That's interesting, since you cannot configure Dell servers with SSDs unless you add a HW RAID card. I believe the reasoning was that the RAID controllers on-board cache could help deal with some of the problems with the current generation's write performance. –  Chad Huneycutt Aug 7 '09 at 23:21
    
You will get some performance hit, even RAID1 will run slower with SSDs, as the drives are generally faster than the controllers. Just the same, faster than HDD (even 15K drives), and will usually be offset by redundancy. I've read a few places where hardware failures with SSDs are about the same as HDD rates in the last couple years. So best to be safe. –  Tracker1 Apr 27 '12 at 18:48

Is it worth using a RAID with SSDs?

In general: yes. For data redundancy, RAID 1 or greater is the way to go. Now, with SSDs, I'm not sure how this affects their performance but I can't imagine it being too detrimental. I don't have experience with SSDs so I can't speak to it.

It seems like the major cause of mehanical failure will have been eliminated by using the SSD

Logically, yeah. But some people are reporting performance problems with SSDs over time. Basically SSDs are still not 100% mature for the consumer market IMO. I can't wait for the technology to mature but when you have problems like this from Intel, and performance degradation it's only a matter of time until manufacturers work out the kinks an outmatch their lowly "disk"-based hard drives.

.. so you're basically trading "Chance of SSD failure" for "chance of cheapo motherboard raid controller failure".

Good point, but cheapo motherboard raid controllers affect both SSD and HDD so it's really a matter of the hardware RAID.

I'm not sure if that's worth it.

Now we get to the meat of your question. Are SSDs worth the money? For speed, without a doubt I think they're worth it. Unless you want a WD Raptor at 10,000rpm, SSD is so much faster. But you said...

I'm worried about the drive having some sort of mechanical failure and losing my data.

I think it's safe to say, just wait. Wait for at least 12-18 months until the manufacturers mature their product lines, prices come down, capacity increases, etc. etc. There's no harm in waiting in the computer industry. Your emphasis is on data redundancy, not speed. Why risk it? And the disks today are so cheap and offer more capacity, if you absolutely need storage today, get cheaper SATA II HDDs and hardware RAID them. You'll probably spend less money overall and when the time comes for SSD, you'll already have a good RAID controller (assuming you put the money into it).

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I just RAIDED 2 Kingston V series 64GB SSDs, and I am getting a speed of nearly 500MB/s. I was curious about RAIDING the one 64 Kingston I have been using as my Boot/App drive for the past month, but this is twice as fast in my Mac Pro 2.8GHz, 12GB RAM,early 2008 Model - "Harpertown" Dual Processors (8 cores). I'm one happy camper !!!

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Bruce, what RAID level are you running? –  Cowmix Jan 15 '11 at 0:56
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I'll bet it's RAID 0. Y'know, scaryraid. –  Tom O'Connor Feb 10 '11 at 10:40

If you do not need too high sustained write performance, you could even go with asymmetric raid1 (--write-mostly), with the other mirror residing on a HDD partition. This had very nice performance for us in a read-intensive database application, it should also play nice as a root or usr partition. However, I would not use this setup for swap or anything similarly write-intensive (swap is dangerous for MLC SSDs anyway).

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