SAS speeds?

By jake ·
Okay i have been trying to expand my knowledge of the different I/O options and speeds. I understand that ATA 133 is only slightly slower than SATA 1 (1.5Gb/s) and that SATA II/III (3Gb/s 6Gb/s respectively) are much faster than the drives themselves can read or write. I understand that most high performance drives can write at 130 or so MB/s, and the reason SATA II came about was more for SSD's with throughputs of 200MB/s.. but what about SAS drives? they are available in 10000 and 15000 rpm options, does that make the throughput of the drives significantly quicker? I would hope and expect that these expensive (by comparison to a standard SATA) drives would be able to move significant amounts of data much faster than a standard disk. And if they dont, then why use them?
This may be a silly inquiry, but i am curious on the matter...

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They have better access time

by jblack In reply to SAS speeds?

This is my opinion --- I've not done heavy research but this is what I've come to find:

In terms of sequental throughput, they may not be much faster (I haven't looked in a while). The advantage that 10K and 15K RPM drives have over 7.2K RPM drives is the access time. They can get to any part of the drive faster than a 7.2K RPM drive. Generally files on a drive aren't in sequential order (Sometimes chunks of files are), so in terms of random throughput the 15K is going to be faster. I've also heard 15K drives make a big difference with databases.

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from my understanding....

by ---TK--- In reply to SAS speeds?

It isn't necessarily about throughput its about the Average Seek time, Average Latency, and cache... If you compare those three you will see that the speed of the SAS drives is much faster than the average HDD, by far. Then take the three SAS slap them in a RAID 5 and throw a massive database on them... and your database is going to fly.

Why doesn't big business use SSD's in their systems? SSD's might have the speed, and through put, but they have a limited life of read/write. If you took 3 SSD's threw them in a RAID, and hosted a Database on that RAID, yes it will be fast... but if 500 people are using that database all day long... How long would that last? A week or two before you had to start swapping drives?

So, I guess my point that I am trying to get at is that even though SAS and SCSI drives might not have as much throughput, it doesn't really matter... the other aspects of the drive makes up for it.

Hopefully that made a little sense...

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