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The price difference between SATA and SAS is really very big. Of course I understood, that SAS drives have their advantages, but does this really legitimate a price difference of 100% or more? Should I really spend 1 Euro per GB?

Of course I understand, that this comes down to my usage of servers. But in may case we are not taking about high performance computing, but merely file servers and web servers etc.

I tried to find some information about this topic, and it came down to the following: (I did not find statistics, that back up any of that)

A) SAS Drives are better in big numbers B) The SAS Protocol is superior and allows more control and optimisation C) The quality of the SAS Drive is also expected to be better, as those drives are produced for enterprise market (of course I am aware, that SAS does not mean, that a Drive has a better quality) D) Drives with higher speed are available for SAS.

Now for my scenario, the prize for SAS seems insane. I need some big storage for educational videos and text-books - and for the price of SAS I might be able to buy triple or even quadruple of the storage.

Further I am applying RAID 10 and backup (both onsite and offsite) - So I think we are pretty safe...

Nevertheless there are two things, that should be considered:

Bottleneck-Situation: I want to avoid the situation, where I buy a nice and fast server, that again has a bottleneck, which might be the drive. And we will have scenarios, where we want to use .

We have enough RAM - 64 GB per Processor - so our will completely fit into the RAM. The speed of the Hard-drives is more important for the serving of files and flash-streaming.

Reliability: Of course, these hard-drives will run 24/7 - so do give SAS such a big PLUS in reliability? I have read different opinions - also in this platform - mostly backed up anecdotical (e.g.Warranty for SAS 5 years, for SATA 2 years - but than another person found the opposite case ;-))

How I see it now, we should stay away from real SAS - and use NL SAS and rather buy another storage unit.

ewwhite
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ChrisZZ
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2 Answers2

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Yes, SAS drives are worth the cost. Error-correction, the SAS protocol and more predictable failure modes give SAS drives an edge over SATA.

If those reasons aren't compelling, you can certainly use SATA, but design for eventual failure. Use a robust RAID level and try to avoid the mixing SATA and SAS disks on SAS expanders (if possible, try to avoid expanders entirely).

See: How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

Community
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ewwhite
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    Hardly a day goes by around here without a question from someone trying to recover a RAID array of SATA disks where something went wrong in the recovery. I wouldn't chance it for anything remotely important. – Michael Hampton Dec 03 '12 at 21:22
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    Technically, he said he would be using NL-SAS which would still use the SAS protocol. While the mechanics are the same, it does provide some of the benefits of SAS over pure SATA. Perhaps the original poster should clear up his post and/or we could provide a full comparison between SAS, NL-SAS, and SATA :) – Rex Dec 03 '12 at 21:33
  • Yes, we are thinking about NL-SAS - but as from my understanding, that is a SATA Drive with a SAS Interface. So it has some benefits - but the drive mechanics are the same. We are talking about 6-12 hard drives per server - more for the backup machine - the backup machine would be really impossible with SAS - but it is only for backup and must not run 24 hours - so I guess it is fine there. We are always using RAID... – ChrisZZ Dec 03 '12 at 21:38
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    Nearline SAS is good. The error-correction, SAS protocol and failure mode issues are all resolved with NL-SAS, even if the physical drive mechanics are similar to SATA. – ewwhite Dec 03 '12 at 21:40
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When you say "SATA", I get the sense that you're actually saying "7.2k RPM drives". These days, most 7.2k drives you'll find on the market use the same interface as SAS drives, so the only real difference is the speed and size.

10k or 15k RPM drives have less space but go faster than 7.2k drives. It takes more spindles to make a RAID of 1 TB, and each of those spindles will have a lower seek time and be able to sustain a higher number of IOs per second, assuming you're straining the disk by doing random small block IO.

Most of the time that people use 7.2k drives, they need the large storage space (as much as 3TB per drive, on my SAN). That said, I can't use these to power my large production oracle database because it drives too many small block random reads, and is very sensitive to the latency you'd see if you try pushing too many IO/s onto too few 7.2k spindles. I certainly use it for my backup servers, though. Also the newest version of Exchange is perfectly happy on slow disk, as are a lot of the volumes on my NAS.

Basil
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