Author Topic: SAS Drive Vs SATA Drive Differences, Technology and Cost  (Read 1189 times)

saroop

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SAS Drive Vs SATA Drive Differences, Technology and Cost
« on: May 04, 2014, 06:56:44 PM »
Hi,


1. Capacity:

SATA (or now called NL-SAS for Nearline SAS) disk drives are the largest on the market.  The largest SATA/NL-SAS drives available with widespread distribution today are 3TB.
SAS disk drives are typically smaller than SATA.  The largest SAS drives available with widespread distribution today are 600GB or 900GB.
So, for capacity, a SATA/NL-SAS disk drive is 4X-5x as dense for capacity than SAS.
A good way to quantify capacity comparison is $/GB.  SATA will have best $/GB.



2. Performance:

SATA/NL-SAS disk drives spin at 7.2k RPMs.  Average seek time on SATA/NL-SAS is 9.5msec.  Raw Disk IOPS (IOs per second) are 106.
SAS disk drives spin at 15k RPMs.  Average seek time on SAS 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.


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

MTBF is mean time between failure.  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/NL-SAS 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.



Regards
Saroop

abhilash

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Re: SAS Drive Vs SATA Drive Differences, Technology and Cost
« Reply #1 on: May 16, 2014, 06:40:24 AM »
Hello,

SAS drives are able to rotate so much faster (up to 15K RPM) than SATA drives (typically 7.2K RPM), seek times may be substantially faster by more than 2 times. 
 While SATA is the least expensive drive available, for servers, it is typically much better to go with SAS for low capacity use cases.  For example, a 10K 146GB SAS drive is not much more expensive than the substantially slower 146GB 7.2K SATA drive.
At higher capacities, high performance SAS drives climb in price steeply.  It may be better to take advantage of dedicated storage infrastructure such as Network Attached Storage (NAS) or a Storage Area Network (SAN), rather than populate a server with expensive direct attached storage.

Thanks