Reference: http://lewanps.wordpress.com/2009/09/14/sas-vs-sata-differences-technology-and-cost/

SAS vs. SATA Differences, Technology and Cost

One of our resources at HP Lefthand Networks (thanks Ben!) made the following comment to one of our customers and I thought it’d be a perfect post for the blog as it contains some useful information that some might not be aware of.

Here are the high-level differences between SAS and SATA disk drives:

Capacity:

• SATA disk drives are the largest on the market.  The largest SATA drives available with widespread distribution today are 1.5TB-2TB.
• SAS disk drives are typically smaller than SATA.  The largest SAS drives available with widespread distribution today are 450GB.
• So, for capacity, a SATA disk drive is 3X-4x as dense for capacity than SAS.
• A good way to quantify capacity comparison is $/GB.  SATA will have best $/GB.

Performance:

• SATA disk drives spin at 7.2k RPMs.  Average seek time on SATA is 9.5msec.  Raw Disk IOPS (IOs per second) are 106.
• SAS disk drives spin at 15k RPMs.  Average seek time on SATA is 3.5msec.  Raw Disk IOPS (IOs per second) are 294.
• So, for performance, a SAS hard drive is nearly 3X as fast as SATA.
• A good way to quantify performance comparison is $/IOP.  SAS will have best $/IOP.

Reliability: there are two reliability measures – MTBF and BER.

• MTBF is mean time between failures.  MTBF is a statistical measure of drive reliability.
• BER is Bit Error Rate.  BER is a measure of read error rates for disk drives.
• SATA drives have a MTBF of 1.2 million hours.  SAS drives have a MTBF of 1.6 million hours.  SAS drives are more reliable than SATA when looking at MTBF.
• SATA drives have a BER of 1 read error in 10^15 bits read.  SAS drives have a BER of 1 read error in 10^16 bits read.  SAS drives are 10x more reliable for read errors.  Keep in mind a read error is data loss without other mechanisms (RAID or Network RAID) in place to recover the data.

Here are some good links for comparing disk types:
http://www.seagate.com/docs/pdf/datasheet/disc/ds_barracuda_es_2.pdf
http://www.seagate.com/docs/pdf/datasheet/disc/ds_cheetah_15k_7.pdf
http://h18004.www1.hp.com/products/servers/proliantstorage/drives-enclosures/index.html

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