Hi

I have a couple of questions i would really like to get some answers to regarding IDE/SATA/SCSI drives and hot-swapping.

Are IDE drives hot-swappable ? I have read that they do not support hot-swapping at all, but would like to have this confirmed by the smart people in here I have heard that the Linux kernel does support hot-swapping but the IDE drives does not, true?

The same questions goes to SATA drives, but i have read that these are hot-swappable, but that this is not very stable (it will probably freeze or crash the hard drive as well as the whole raid array if it would be done), true?

I know SCSI drives are hot-swappable, but i have also read that this can be a little unstable as well.. what i read was that even though hot-swapping was possible the drive froze and the whole raid setup failed. Is this a "one-in-a-million" situation or does hot-swapping function well with SCSI drives?

All help i greatly appreciated, thanks for sharing your time to help me.

IDE drives are not hot swappable. Let me give you some insight into the hardware. For any device to be hot-swappable, the hardware as you plug it in, has to make ground first, then power, then logic pins. When you remove a hot swappable device, you break signal, break power, then ground.

This means the pins on the interface must be different lengths. Look at any IDE drive, pins are the same length.

Now, there are some drives with modified pin arrangements, and are hot swappable. I have seen them on IBM mass storage devices. You won't see these things on desktop systems.

The linux kerenls now support hot swapping. PCMCIA cards can be hot swapped. USB devices also.

SCSI? Not that I ever saw. I don't see much SCSI on PC's these days. Larger systems yes, not desktops or lap tops.

Thanks for you answer. Hmm, ok. I just read that SCSI devices isnt hot-swappable either and based on your reply that seems to be true, but i think i have seen serveral times in data centers that you have hot-swappable harddrives which you can just take out and in again. Im not talking about laptops or desktop systems here when it comes to SCSI although you could of course buy scsi and set up a nice raid home but its quite expensive.

SATA, SCSI and SAS (Serial attached SCSI) devices can all be hot swapped IF the controller they are connected to supports hot swapping.


3ware makes a line of SATA controllers that support Hot Swap
http://www.3ware.com/products/serial_ata9000.asp

SCSI4me sells a bunch of drive cages for hot swap setups.
http://www.scsi4me.com/sata-serial-a...nal-cages.html

If the controller cards does NOT support hot-swap then do NOT hot swap drives from the controller.

your bargain el-cheapo controllers will NOT support this feature. you will have to spend a few bucks to get this capability.

Great answer farslayer Is there any IDE controllers that will support hot-swapping as well?

Yes there are.. Again check 3Ware for controllers that support that option. the scsi4me site I referenced above will also have PATA drive cages for hot swapping PATA drives.

If you are just starting out with a new setup I would recommend going with SATA though rather than PATA. Some of the better SATA drives support features you would want for an array such as NCQ (Native Command Queuing). I don't believe those features are available on any of the PATA drives.

http://www.3ware.com/products/parallel_ata.asp

If you are going high-end, SAS Drives seem to be the hot ticket lately.


Serial ATA (SATA) Linux hardware/driver status report


the 3ware cards I linked to are true Hardware RAID controllers. fakeraid and software RAID controllers will not have the hotswap support.
http://linux-ata.org/faq-sata-raid.html

Okey. Then im just wondering of couple of things. The controllers, IDE/SATA/SCSI, does hot-swapping work OK on these that support hot-swapping or should you avoid hot-swapping? I mean, when you for example have a hardware raid of IDE disks, is it safe to do hot-swapping.. there isnt any big chance that the disks are freezing or crashing is it ? Does hot-swapping work better on scsi drives than ide drives or is it the same?

Hot swapping is an enterprise feature. If I have a production server that has a drive failure in a RAID array, I can remove the dead drive, replace it with a new drive and rebuild the array (often the rebuild is automatic on the insertion of the new drive) With hot-swapping capabilities I do not have to take the production server off line to get the RAID array repaired. for a home system this feature may be a bit of overkill.

I've never run into an issue replacing a dead drive in this fashion. but remember the limitations of RAID. You can only hot swap ONE drive from a RAID 5 array at a time and then you have to wait for the array to rebuild before you can swap another drive without crashing the array. that is a limitation of RAID 5 rather than the controller. Hot swapping originated with SCSI drives but seems to work just as well on other drives now, provided it is supported by the controller.

Thanks for your answer, that made it more clear

There are SCSI, SATA, and SAS hot swap drives. The controller and drives are typically specially designed for hot swapping. All Linux distributions would support it but you have to make sure to unmount the device and any partitions prior to removal. This will insure the system isn't flooded with IO Errors as the system loses the device.

In the case of a hardware RAID 5 array there would be nothing to unmount, since the system will see the entire array of drives as a single device, so you would simply pull the defective drive and replace it on the fly. After which the controller will either automatically begin the rebuild or you would have to use the array management software to manually start the rebuild process.