Hot-swappable SATA Drives in RAID 5 on Linux?
 

Is it possible yet? How about with NCQ?

For NCQ see the "Linux SATA Hardware status" -> http://linux.yyz.us/sata/sata-status.html
Lookup up your controller. Some controllers supports ncq some other don't.

For Hotplugging see the "Linux SATA Software status" ->
http://linux.yyz.us/sata/software-status.html#hotplug

It says that you can't take the drive out yet.

Well, thats the whole point of hotplug, especially with raid 5 or 6.

Yes, it is just that libata isn't finished yet, so some things are not yet written.
I believe that when i was playing with some kernel patches i caught my eye in a patch
that implemented hotplug but is not in mainland libata yet. Search jgarzik directory
in your kernel.org mirror.

Just out of curiosity, does anyone know when they plan on completing it? We're thinking of building a small NAS for the office using linux but clearly hot swap is necessary. Also, if the drive is in a hot swap enclosure, does this make a difference in whether or not you can hot swap it? Thanks for your time.

PS. Also, is hot swap support being developed for PATA, SATA I, or SATA II? According to this thread: http://www.linuxquestions.org/questi...highlight=sata
only the SATA II interface allows for hot swapping. Is this true? Thanks for your time.

You could use SCSI. I'm pretty sure Linux has good SCSI hotswap implementation.

Synesthesia, any links pertaining to SCSI hotswap support on Linux? Thanks for your time.

A variety of hopefully helpful links:

http://www.ram.org/computing/linux/dpt_raid.html

http://www.tldp.org/HOWTO/Hardware-HOWTO/scsi.html

http://www.linuxjournal.com/article/2391

http://www.linuxjournal.com/article/5653

http://linas.org/linux/raid.html

http://www.tldp.org/HOWTO/Software-RAID-HOWTO-4.html

Have a look at 3ware SATA-I and SATA-II controllers. The kernel does support the latest SATA-II controllers from 3ware but you need kernel version 2.6.14.

I suggest you do not mess with software RAID level 5 and 6 because it will put a very huge load on the computer if the system does not have multiple processors.

Using NCQ will slow the RAID-5 down, so only use it for RAID-1 or single drive systems. If you want the system to access multiple files at once, put two hardware RAID-5 arrays in software RAID-1. Buying a hard drive with the biggest cache will not help in RAID stripping levels. I do not think the hard drive cache is ever used in Linux anyways.

Thanks for the links Synesthesia. Electro, what are you experiences with RAID 5 or multiple RAID 5s in terms of CPU usage? On what CPU did you have the RAID configuraton and how much CPU usage did the RAID 5/6 take up? Also, would using a dual-core AMD64 processor be more than enough to handle the load?

I am sorry, but I do not use RAID. What I have seen from benchmarks at several sites with software controllers (Promise and Highpoint) that includes RAID 5 support (for Windows only) perform poor even though they have onboard XOR and some cache. One reason for this is high processor usage. Hardware RAID controllers such as 3ware and Areca perform very well.

You can go with software RAID-5 or RAID-6 with a dual processor system like the Athlon64 X2 but the I/O throughput is going to be worst than going the hardware RAID controller route.

I know its not linux oriented, but this is a nice read: http://www.tomshardware.com/2006/01/...d_controllers/