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bbeermat

Why not RAID 1 with an SSD and a Raptor?

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I've never seen this tested but I'm guessing it would give very high performance? Most data retrieval will begin from the SSD, giving low access times, then when the Raptor catches up, the transfer rate will go up. Not sure if this would work for writes, as the SSD would always be limited by the hard drive, correct? Anyone have an SSD to try this out?

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I've never seen this tested but I'm guessing it would give very high performance? Most data retrieval will begin from the SSD, giving low access times, then when the Raptor catches up, the transfer rate will go up. Not sure if this would work for writes, as the SSD would always be limited by the hard drive, correct? Anyone have an SSD to try this out?

IMHO, it would be better to just put two Raptors in RAID 1, as the inexpensive SSDs that are currently available still can't match the performance of a Raptor, and using an SSD effectively limits the available space to the SSD.

Alternately, put 4 - 8 Raptors in RAID 1+0 for really high performance. :)

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Generally with any RAID level that involves parity if one drive is slower than the other, you're limited by the slowest drive, so that combo probably wouldn't work as you expect. The Raptor would be slow to seek/access the data, but the SSD wouldn't. The SSD will be way faster accessing/seeking, but slow to write (typically, though they're getting better).

I agree with Trinary that SSD's aren't fully matured yet. I'm intrigued by what they offer, but they're not totally prime time ready at the moment.

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I'm more worried by their limited write/rewrite cycles. Putting a swap file on one would be unwise...

True SSDs (as opposed to just flash-cards and whatever) have wearleveling algorithms so in theory you can write at full speed for 10 years or something before hitting their "limited" write/rewrite cycles

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Although if you note, most SSDs don't have super-long warranties as you'd expect, which makes me wonder how much faith their makers have in their write cycle leveling...

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Generally with any RAID level that involves parity if one drive is slower than the other, you're limited by the slowest drive, so that combo probably wouldn't work as you expect. The Raptor would be slow to seek/access the data, but the SSD wouldn't. The SSD will be way faster accessing/seeking, but slow to write (typically, though they're getting better).

I see what you're saying, but in a RAID 1, during reads, whichever device retrieves the data first will immediately begin doing so, then when the other one catches up, data will stream from both devices. That's why RAID 1 is supposed to be be as fast as RAID 0 on reads, right? Possibly controller dependent? I thought performance on would be limited to the slowest device only on writes.

Say you have lots of small files that need to be loaded and they're scattered over the 'disk', such as when booting or starting most programs. That will be fast because of the SSD low access times, even though the Raptor may never catch up under that scenario. Once you load a 'big' file, the Raptor will catch up, and it's high transfer rate will be added to the SSD's transfer rate.

Remember we're only talking about reads here.

How about 2 SSD's RAID 0, in RAID 1 with a Raptor to boost writes?

Hope my ramblings makes sense. :P I just really wish I could try it.

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Well, the theory sounds good, but I'm guessing it's dependent on how the individual RAID controller implements things. Still, writes are going to be limited to the slowest drive, whatever that may be. It shouldn't be a big issue if your RAID controller has a big cache on it, but it could still come into play. You're going to hit that write speed limit on the SSD pretty quick if you try to write a 20GB file to an SSD/Rapter RAID1.

For reads, I imagine you would get the best of both worlds on a decent controller.

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Veritas is doing research with RAID 0 vs large caching and they're initial results have shown that it's better to get a larger cache than another disk for raid 0. I haven't seen numbers yet and I heard about this a long time ago from one of their members. Don't know what the state of their research is at this moment.

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