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eSATA port multipliers for Mac OS X
Since I have seen more and more storage products lately utilizing SATA port multipliers, I decided to do a little research on the topic.
SATA port multipliers
Official home page for the standards body
-ratified standard.
-multiplexes several (up to 15) SATA links over a single physical connection. Total bandwidth is still limited to the current 300MB/s that SATA II allows.
-is convenient because it allows for a single eSATA cable to connect to a storage array of multiple drives, instead of having to have one port per drive as with the normal SATA specification. Non-PM storage systems require a SATA or eSATA cable for every drive in the enclosure, an ungainly and impractical system to scale.
-any SATA hard drive will work in a PM configuration. As far as the SATA hard drive knows it is the only drive on its bus.
-must use a port multiplier-aware host bus adapters
One question I had was will port multiplying solutions sacrifice speed? Even though multiple drives are sharing a 300MB/s link, that is enough speed to service the bandwidth requirements of 3-4 of the fastest SATA hard drives. For comparison:
The fastest SATA hard drive, the Western Digital WD1500 Raptor, can transfer at best 88.3MB/s.
http://www.storagereview.com/articles/200609/ST3300655LW_2.html
The fastest hard drive of all, the Seagate Cheetah 15K.5 can transfer at best 135MB/s, but it is not available as a SATA drive.
Cabling – SATA vs. eSATA
It is important to note that SATA and eSATA cabling are separate and distinct specifications. Electrically they are the same, but eSATA cables are more durable and are better shielded for environments outside a computer case. eSATA connectors are physically different and will not work with SATA cabling and connectors. SATA connectors are only designed to withstand 50 insertion and removal cycles, while eSATA connectors are rated for 5000.
http://www.sata-io.org/documents/HowtoselecttherighteSATAconnectorandcabler11-fc2.pdf
This can be an issue when you are specifying a storage system for a customer and you fail to check the connector type on the host adapter and the storage enclosure. I have found that it frequently isn’t clearly specified in the marketing materials or specs, and some manufacturers have been using SATA connectors where they shouldn’t be. Double-check it if you aren’t sure!
Multi-Lane Cabling
Serial ATA x4 connector system. Connector standards defining SATA cables that contain 4 “lanes” of SATA connectivity. Specifications exist for internal and external variants.
The SATA standards organization, SATA-IO, controls the SATA electrical and mechanical specifications.
Products that use SATA PM:
CalDigit Fusion 500P
-note: I spoke to a couple of people at PowerMax and they have very favorable things to say about CalDigit. We have established reseller agreements with them and apparently they are good to deal with when it comes to RMAs, pricing etc. Unfortunately you can’t order their enclosures “empty” so keep that in mind.
-Ross and I have encountered a couple of these in the field that have had poor reliability. It is unclear if it was caused by the enclosure or the Sonnet Tempo host bus adapters.
Unrelated but cool
Check out the Ciprico Mediavault 4400:40 (!) 2.5″ (!) SATA hard drives in an enclosure with 4×4Gb Fibre Channel (!) connections. 800MB/s to 1200MB/s sustained transfer rates (!!!)hard to find pricing but appears to be in the ~$30,000 range, but you need that throughput for 4k/2k editing.
References:
http://www.bellmicro.com/resources/downloads/3Barbara.ppt
http://www.spoerle.com/binaries/1134744766182-E357_Molex_SAS.pdf
http://www.scsita.org/aboutscsi/sas/SAS_IG.pdf
SATA standards body
Posted in Hardware