Novice question about hot swapping

[lovehate]

Greetings all! I would like to acquire a NAS but I have this puzzling question about hot swap.

If I run any kind of RAID(not including RAID 0) and I did a hot swap, will it be considered that the HDD that I swapped out has failed and data will be re-constructed into the new HDD that I plug in?

If I do not run any RAID, I do a swap, I will not be able to access whatever files in the HDD that I swapped out but I can access the files on the new HDD that I had swapped in right or does hot swap has to go with RAID?

Assuming that the NAS supports hot swapping.

 

[davidktw]

Greetings all! I would like to acquire a NAS but I have this puzzling question about hot swap.

If I run any kind of RAID(not including RAID 0) and I did a hot swap, will it be considered that the HDD that I swapped out has failed and data will be re-constructed into the new HDD that I plug in?

If I do not run any RAID, I do a swap, I will not be able to access whatever files in the HDD that I swapped out but I can access the files on the new HDD that I had swapped in right or does hot swap has to go with RAID?

Assuming that the NAS supports hot swapping.

Hot swap has nothing to with RAID. For controllers and systems that support hot swap, it means you can remove the harddisk from the controller without damaging the controller and also the hard disk, while everything is running. However, you MUST unmount or detach the filesystem that the harddisk is running on. Hot plugging away the device basically inform the OS that the device is missing, but filesystem will get tons of I/O errors such situation and can result in kernel panic.

For filesystem riding on top of a RAID volume, the filesystem is not directly on the device but a layer on top of the software or hardware implementation of RAID, hence when you unplug the harddisk, you do not need to umount the filesystem if the underlying RAID layer can continue to function without the missing device(s). Basically the RAID implementation be informed by the controller that the devices have failed.

Replacing the new HDD into the system will inform the OS of the device present, the RAID controller or S/W RAID implementation will react as accordingly. Without RAID layer involve, the OS basically is informed of the new device will not do anything, though I suspect there is automounting involved if configured to do so on unix system.

 

[lovehate]

Replacing the new HDD into the system will inform the OS of the device present, the RAID controller or S/W RAID implementation will react as accordingly.

Thanks for that explanation. Get it about hot swapping device away. So what you meant by the above quote would be that it depends on my RAID H/W or S/W?

Keeping it simple, let's say that I have a 2 bay NAS running RAID1. I hot swapped the HDD in bay2. Will the controller re-construct(mirror) everything in bay1 into the new HDD in bay2 as it deemed the previous device has failed or only new files will be mirrored into bay2?

This would also mean the same goes for any other RAID(except for 0)?

 

[davidktw]

Keeping it simple, let's say that I have a 2 bay NAS running RAID1. I hot swapped the HDD in bay2. Will the controller re-construct(mirror) everything in bay1 into the new HDD in bay2 as it deemed the previous device has failed or only new files will be mirrored into bay2?

This would also mean the same goes for any other RAID(except for 0)?

RAID 0 has no redundancies, therefore we can put that out of the topic. For this array configuration, most likely a kernel panic will happen within a short while depending on whether there is read and/or write that map to the device.

Other RAID configurations, where your controller and OS support hot-swap will allow you to remove and plug in a new device. Automatic resilvering will depends on your RAID configuration, it doesn't have to happen automatically. Some requires user to initiate the resilvering process manually, but it shouldn't be of great concern to you unless you are in an enterprise environment where things need to be automated. In such cases, we will use hot-spare configured into the RAID array. Most consumer RAID systems have greatly simplify the operations to this this use case, so it shouldn't be of great concern to you.