Friday, March 30, 2012
Here are the high-level differences between SAS and SATA disk drives:
- 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.
- 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.
Monday, February 20, 2012
ICC - Integrated Circuit Card (aka smart card)
IFD - Interface Device (aka smart card reader)
There are variety standards or methods for such. Among others are ISO 7816-4, EN 1546, and Unilateral Authentication. The following table displays an example of mutual authentication according to ISO 7816-4 standards.
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A figure XIFD is sent to ICC to decrypt. XIFD is the encryption of Master Key KIFD which is the combination of seed keys from both IFD and ICC (RNDIFD and RNDICC ).
XIFD will be decrypted at ICC to obtain the value of Master Key KICC , which will then revealed the calculated seed keys (RND’IFD and RND’ICC ).
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RND’ICC = RNDICC ?
The calculated value RND’ICC is compared with RNDICC . If seed keys matched, ICC regards IFD as a trusted source.
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A figure XICC is sent to IFD to decrypt. XICC is the encryption of Master Key KICC which is the combination of seed keys from ICC (RNDICC) and calculated seed key of IFD (RND’IFD). This time, the arrangement of the seed keys has been reversed.
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XICC will be decrypted at IFD to obtain the value of Master Key KIFD , which will then revealed the calculated seed keys
(RND’ICC and RND’IFD ).
RNDIFD = RND’IFD ?
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The calculated value RND’IFD is compared with RNDIFD. If seed keys matched, IFD regards ICC as a trusted source.