Thursday, February 26, 2015

hard drive - Desmistifiying SATA hotplug

I have a BIOS that has an option to enable hot-plug on individual ports. I have a sliding enclosure for HDD and SSD (nothing more than a pass-trhu to power and a sata port) that allow me to cut power to the drive before physically moving it.



I would love the convenience of inserting and removing HDD/SSD there without shutting down the computer every time.



But while researching about SATA hotswap, out of expensive enterprise solutions, there is zero reliable information. I tried even looking at patents. I can't find a single reliable source that tells me how reliable/unreliable is hotswapping on the consumer world.



So, I do have support in my bios, motherboard and enclosure. The drivers I've never seen mentioning hot-pluggable on the specs, even on the enterprise ones. How much risk of data loss will i be facing for this convenience?



Then, hardware aside, there is the software issue. Do i need support on the OS? and is there any AT command to unplug the drive that must be issued or does it park it's head on power down automatically? there is a slightly informed discussion on the software side here







edit:
found some more info regarding hot-pluggable. from Western Digital: it says every driver that supports SATA by definition of the standard, already support hot-plugging.




SATA-compliant devices thus need no further modification to be
hot-pluggable and provide the necessary building blocks for a robust
hot-plug solution, which typically includes: Device detection even

with power downed receptacles (typical of server applications)



Pre-charging resistors to passively limit inrush current during drive
insertion



Hot-plug controllers to actively limit inrush current during drive
insertion




source: http://wdc.custhelp.com/app/answers/detail/a_id/941/~/hot-swap-or-hot-plug-wd-sata-drives







But, the above starts another doubt. it says:




In order to take advantage of hot-plug capabilities for your Serial
ATA hard drive, you must use the Serial ATA power connection, not the
Legacy (Molex) power connection. The Legacy (Molex) power connection
does not support hot-plugging.





some of my drivers are connected from molex->sata power, just because i'm out of sata power ports on my PSU. from what i could trace, some molex and Sata power comes from the same 12V rail. and the SATA plug does not have any logic it seems. it is just dumb plastic. Does that mean i'm safe and the doc refers to drivers that supports both sata and molex?

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