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SSD in RAID-0 / MTBF / Multi-channel / Bus saturation / Concurrent performance

Posted on 2009-05-03
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Last Modified: 2012-06-27
I am considering how to optimize and build the fastest storage I can into a new workstation. See question here where I discuss with garycase : http://www.experts-exchange.com/Hardware/Desktops/PCs/Q_24376828.html#a24292477

I've read all I can find on SSD, and I know the listed MTBF are listed 1.2 million hours for the X-25 E that I am considering.

What are the practical MTBF for 2x RAID-0? I know how to compute traditional failure factor, I multiply the individual components, but I am curious of MTBF applies with SSD in the same way as platters. Why? Because with platters, often failures are due to g-shock or vibration or head crash. This doesn't really apply to solid state, so are the MTBF of 2 drives to be calculated the same, or are MTBF in SSD more describing the "life" of the drive, given typical use (ie. given the cell life of the flash, and the allocation/fragmentation algorithms).

I can go with 2x SSD RAID-0 if I feel a single SSD is as reliable as an old platter RAID-1 mirror. What do you think?

If so, what RAID card might I consider, and should I consider a multi-channel card, so the RAID spans channels?

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Question by:mrjoltcola
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by:_
_ earned 200 total points
ID: 24292678
>> But we agree that with enough RAM, and knowing your applications needs, it is possible to do it.

I will give you that one.   ; )

>> I am curious about affecting the life / fragmentation of the SSDs if I swap to it, though. I read that the X-series intel models had a fragementation problem and some people see slowdown after a while

Fragmentation isn't really a problem with SSDs, as there is no 'seek time' to speak of.
From what I have read, the 'slow down' most people refer to is that when these drives write, they do it in blocks, and they have to erase that block before they can write it back .  So when you do a lot of 'file editing'  it can seem to slow down, as compared to writing to a fresh drive.

The firmware upgrade is basically just a better algorithm to spread the writes out so that the 'wear' on the cells is even, and keep better track on where the 'pieces' are stored.
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garycase earned 250 total points
ID: 24292683
Send me two 64GB X-25 E's and I'll do plenty of experimenting for you :-)

A bit more seriously ... MTBF is a statistical measure (as you know), so the mathematician in me says it still computes the same way, since failures tend to be random in electrical components.   But as you've noted, there's also a mechanical component to failures in rotating platter drives, but not in SSDs.   Consequently, it's probably reasonable to assume that the MTBF of a pair of SSDs would likely be close that of a single unit IF you were past the infant mortality period (clearly you double your risk of infant mortality)

I do, however, think a RAID-0 pair of SSDs is even more reliable than a RAID-1 of platter-based drives.   By the way, with the current pricing of the Intel X25-E drives, you can build a 64GB RAID-0 pair for the same price as a single 64GB X25-E -- so if you have the RAID controller and space for the drives, this would give you better performance for the same cost (same access time; better transfer rate -- providing your bus has the bandwidth).    Be sure your RAID card attaches to a bus that has enough bandwidth for the drives you plan to attach.   A PCIe x4 card is likely required if you don't want the bus to be the limiting factor => especially if you're going to use 3 or 4 drives in the RAID-0 array.
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by:mrjoltcola
ID: 24292736
@coral47: I read about the slowdown on newegg, so not sure how credible it is or how commonplace.

@garycase:  >>Send me two 64GB X-25 E's and I'll do plenty of experimenting for you :-)

As busy as I am, I may take you up on it. I have a software project delivery coming up and don't have much time. I'll need this monster built and tuned and probably firmware upgrade and Vista 64 installed and patched. What worries me is I will order the stuff, then have a problem with compatibility and get sidetracked with RMAs. Want to build it and document the process on your website? Payment in form of an X-25? :)


So I am decided on the X-25 E, RAID-1 but not decided on the card. I have a 3Ware 4-Port card in my current box, model 9650SE-4LPML. Not sure if it is multi-channel or not. Basically all I care is that I saturate the bus. It says connector type "multi-lane".

Now to decide on the card, motherboard and memory. I've had good experience with Corsair, but haven't bought a server grade motherboard in years.
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by:Callandor
Callandor earned 50 total points
ID: 24295994
I recently installed one of these http://www.newegg.com/Product/Product.aspx?Item=N82E16820220342 as my boot drive, replacing an older 74GB WD Raptor.  I haven't noticed a speedup in boot time, though it is quieter and cooler, and sometimes it hangs for no reason that I can determine.  It's possible a clean OS would make a difference, as this system had its OS installed over 5 years ago, but I think SSDs still need some more work.
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by:garycase
ID: 24297916
I agree SSDs are not entirely ready for prime time -- but the Intel's are about as good as they get ... especially the SLC versions.   MLC-based drives have far more of the "freezing" issues (especially with Outlook) then the SLC-based drives.   Note that these can usually be mitigated by disabling Window's pre-fretching => have you tried that?
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by:Callandor
ID: 24298788
>Note that these can usually be mitigated by disabling Window's pre-fretching => have you tried that?

I'll try that.  My Outlook pst file is on another drive, since I was aware of that issue.
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by:Callandor
ID: 24332384
I continued to have pauses, so I popped the Raptor back in and things are much better.  I should have read this article earlier http://www.anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3403&p=1, it would have saved me a lot of trouble.  The Intel SSD is a lot better.
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by:mrjoltcola
ID: 24332429
I am ordering a single X-25 E as a test, will post back here to update my findings. Thanks for the input.
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by:_
ID: 24332607
Thank you much.  : )

Have fun with the new toys.   ; )
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