amdoverclocker2

SAS over SCSI?

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What are the advantages, other then mix of SAS and SATA drives, of SAS over SCSI? Ive been looking and the interface doesnt look to be of an improvement with the same internals of a drive, ie Atlas II 15K vs Atlas II SAS 15K. Does SAS have the same weak interface as SATA? If so, that will probally seal the fate of SAS for me. I hate the way the desinged it. The most used part of the drive yet its the weakest part of the drive. Also, I am going to be using external cages on parts of my project, are there any controller that have more then one 4X external port? Two would be nice. Now with that, any reviews of controllers yet? Advice on controllers? Thanks. I will have the servers for this project for about two weeks before they go into production so I plan on testing the crap out of them. Hes a parts list that I have so far: 16 x 36GB 15K drives, 16 x 74GB 15K drives, 14 x 500GB drives, 12 x 280/285 Opterons, and 100GB of RAM. :)

Edited by amdoverclocker2

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I don't think 2.5" 15K drives exist yet. Seagate makes a 2.5" 10K drive, though. The physical media is about 2.5" in diameter, but that'd still be in a 3.5" form factor.

As for the physical interface, SAS and SATA are supposed to share the same connectors, with maybe a key on one and not the other. The idea is to have the flexibility of using a SAS controller to talk to a combination of SAS and SATA drives in a setup.

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Seagate makes a 2.5" 10K drive, though. The physical media is about 2.5" in diameter, but that'd still be in a 3.5" form factor.

I dont think that is true. 2.5" is implying that the entire drive is 2.5" wide. They have hotswap cages that fit 4 x 2.5" drives in a single 5.25" drive bay.

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Oh, I agree. It'd be misleading to say a 15K is 2.5" merely because the media size is that and not the external drive size. Originally, the form factor size *did* correlate to the media size, but that's not true with 10K and faster drives.

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Oh, I agree. It'd be misleading to say a 15K is 2.5" merely because the media size is that and not the external drive size. Originally, the form factor size *did* correlate to the media size, but that's not true with 10K and faster drives.

When was this true? 80's?

SAS connector fits both SAS and SATA ports without keys or special adapters. I will take a photo of mine and post it here for everyone to look at.

Yes. Anything else different? I see no use for it then.

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Oh, I agree. It'd be misleading to say a 15K is 2.5" merely because the media size is that and not the external drive size. Originally, the form factor size *did* correlate to the media size, but that's not true with 10K and faster drives.

When was this true? 80's?

Well, all 3.5" PATA drives and almost all 3.5" SATA (excluding the Raptors) use media that's pretty close to 3.5" in diameter. 95 mm or so, IIRC. And earlier, 5.25" drives used media that was pretty close to that 5.25", too.

But with 10K and faster drives, it wasn't possible to have the high spin speeds and the larger diameters, so you'll see ~ 3" media used on most 10K and something closer to 2.5" media used on 15K.

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What are the advantages, other then mix of SAS and SATA drives, of SAS over SCSI? Ive been looking and the interface doesnt look to be of an improvement with the same internals of a drive, ie Atlas II 15K vs Atlas II SAS 15K. Does SAS have the same weak interface as SATA? If so, that will probally seal the fate of SAS for me.

What do you mean by weak?

As for differences, I'm curious to see some SAS versus SCSI performance comparisons. I do know that SAS has less overhead associated than the parallel bus (reaults of what had to happen to make it backwards compatible with slower SCSI standards). There may be some improvements in workloads with lots of small transfers.

Also, you know SAS is going to phase out SCSI in the coming years so if you plan on using this server for more than 3, it might be better to go SAS. I'm sure SCSI still has a few years life left in it though. Certainly SCSI is the safer path.

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What do you mean by weak?

Weak as in the physical connector of the drive and controller card.

Physically the SAS and SATA connectors are identical. SAS drive connectors may have a few more contacts live.

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Physically the SAS and SATA connectors are identical. SAS drive connectors may have a few more contacts live.

note that an SATA cable cannot and will not fit onto a SAS drive. But a SATA drive will fit into a SAS connector or cable.

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