[OpenIndiana-discuss] Opinions on LSI RAID vs. ZFS

[Edward Ned Harvey (openindiana)]

> From: Christopher Chan [mailto:christopher.chan at bradbury.edu.hk]
> Sent: Tuesday, October 08, 2013 8:42 PM
> 
> Er...isn't hotswap capability PART of the specs whether the drives are
> SAS or SATA? I can do this on a cheap desktop motherboard but you cannot
> on a server board with getting a HBA?

Maybe you're using a different bios, or maybe you're hotswapping like for like drives that coincidentally work in your situation or something, but ... 

In BIOS, I have the option to enable/disable SATA port 0, 1,2,3.  If the port is enabled and nothing connected, it throws and error during POST.  If something is connected, it's identified as a 1TB or whatever drive, and presented to the OS as c1t1d1 or whatever.  Later if I disconnect that drive while the OS is running, the OS still thinks c1t1d1 exists, but if I try to access it, I'll get an IO error.  If it were truly hot plug, then the OS should get a drive disconnected signal, and c1t1d1 should not exist anymore.  As is the case with a USB drive or firewire.

And if I stick a different drive on that line, it *may* behave correctly, but I won't trust it.  The chances of correct behavior are improved if you're swapping the drive for another of the same model, but I seem to recall bad behavior when swapping a 1T drive for a 2T drive or 500G.

If it works for you, I say great.  I only feel comfortable with using something that truly supports hotplug, or rebooting.

PS.  I accidentally fried a mac laptop SATA hard drive once, when I thought the computer was off (it was actually asleep).  I was transplanting the hard drive from one laptop to another, due to a broken screen.  The moment I pulled the SATA hard drive out of the old laptop, while it was still powered on, that hard drive was fried and never again functional.  Wouldn't spin up anymore (or if it spun up, it was never recognized as a drive ever again.)

Back at that time, I looked it up, and found as you said, hot plug is supposedly incorporated into the SATA spec.  But it's poorly implemented, rarely tested, and not to be relied upon, unless you have another layer beneath it (such as truly hotplug capable HBA) which will make up for the deficiencies of the SATA hotplug.  Basically, if your product was *intended* to be used for hotplug, and it advertises itself as hotplug, then it's hotplug.  But if you're just blindly assuming all motherboard internal built-in SATA adapters support it ... you're taking your data into your own hands.