When are Hot-swap hard drives useful?

[William Harrington_1]

SCSI hard drives on Netservers are often referred too as "hot-swapable" however since in most cases these drives are running in a RAID configuration that requires a drive to be rebuilt when it is replaced it does seem that the hot-swap feature is really useful in most cases since the RAID rebuild may require hours of off line time.
Am I missing something or is there actually a situation where a drive is pulled out of a Netserver and replaced and is then usable without rebuilding or rebooting?

[Mahesh Kumar Malik · Accepted solution]

Hi William

You are absolutely correct. When a faulty drive is replaced RAID rebuilds. The basic advantage of hot swap is that drive can be replaced ONLINE i.e. without shutting down or powering off the server thus minimizing the down time.

Regards
Mahesh

[William Harrington_1]

Thanks for the comment but I'm still not sure I understand. I've seen it written that a drive can be replaced and it will re-build automatically but I have not found that to be true. Does the RAID automatically detect a new drive and start a rebuild?

How would I know what drive to pull? Just by checking the activity lights on the front of the drive? The drive with a light that doesn't blink is the bad one, right?

I've had a circumstance where a logical drive failed but it was then rebuilt in the RAID manager without any replacing any hard drives, so how does the HotSwap come into play in that instance?

Do some Raid5 arrays actually rebuild them selves after failure without user help?

Any comment is appreciated.....

[Florian Heigl (new acc)]

Why do You need to rebuild offline?

usually one even has a hot spare drive available, so that the broken disk can swapped out somewhat later (will i.e. save on response time requirement for service contract, thus saves money)

[Mathias Tschachtli]

Hy William
My opinion is that a hot-swap drive is usefull when a rebuild must start quickly after a hard drive is going down and the danger exists that in case of a second loss of a non removable disk the system crash.

If you have set a hot-swap drive for a RAID-Set then the system takes this drive when another drive is going down. Thats true.

Does that answer your question?

[William Harrington_1]

I was missing something... When I asked the question I was thinking of hotswap as a general term and I now realize that hotswap is also a term used specifically in a RAID that puts the drive in a "hotswap" HS position.

Thanks for all your comments, I think I know enough now to be dangerous.