Adding HDD's to Raid 5

E

eagleknight

Limp Gawd
Joined
Dec 8, 2006
Messages
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If I am running a Raid 5 off of a controller card with 3 disks to start with. Is it possible to add a fourth disk to increase the capacity? Does the whole array have to be rebuilt to do this? I have been looking at the RocketRaid cards from HighPoint.
 
That feature is called Online Capacity Expansion (OCE) i believe. Its possible to add drives at later times with RAID cards that have this feature, although from what i hear, to add a 750 gig per se harddrive would take a looooong time to rebuild your array.

Nicer cards have this feature. RocketRaid / HighPoint is a good place to start.
 
Yes! I did find this listed on the feature of the HighPoint cards I have been looking at. Even if it takes a long time it is something you only do once in a great while.

- Online Capacity Expansion and Online RAID Level Migration (OCE/ORLM)
 
Well, id ask others how long its taken on their part, as from what ive heard it can take close to a week to rebuild a large array. but yea, thats the feature youre looking for :)
 
Am I right in thinking with some cards the array is still usable whilst rebuilding?
 
Almost irrelevant but with software raid (md) and a XP1900+ it took 9 hours to expand the array and 6 hours to expand the file system from 3x500GB to 4x500GB. It should take longer the bigger the drives. With this you can use it while it's running but it obviously slows it down. Not sure about hardware... (hence, almost irrelevant reply)
 
Tomson said:
Am I right in thinking with some cards the array is still usable whilst rebuilding?
Click to expand...

Good you asked this. With my Areca 1210 I added my 4th drive to my RAID 5 setup while still gaming. I was amazed at how my system was not bogged down at all. it ran smoothly.

I was just testing it out while doing other things. Not something one would want to do on a regular basis.
 
you even connected power to a hdd while it the system was still live? I'd be too scared.
 
tgrimley said:
Almost irrelevant but with software raid (md) and a XP1900+ it took 9 hours to expand the array and 6 hours to expand the file system from 3x500GB to 4x500GB. It should take longer the bigger the drives. With this you can use it while it's running but it obviously slows it down. Not sure about hardware... (hence, almost irrelevant reply)
Click to expand...

hmm I use xfs file system and takes about 3 seconds to expand.

I expanded from 3 500 drives to 4 then 5 drives longest time took about 12 hours that may have been because the array was full each time.
 
I tried that as a test on my 3ware 9659SE card.
It did the calculations at about 3-4MiB/s which is dead slow on a big array.
On a Adaptec 5805 the speed is about 16MiB/s. I found that out from discussion with another member here recently. That is the new dualcore 1200MHz card.

I can't be sure but I think that during this process your data might be more exposed and at a grater risk of a loss if one of your existing hdd's fails.
Maybe somebody can say more about this.
 
Zefram0911 said:
you even connected power to a hdd while it the system was still live? I'd be too scared.
Click to expand...

That's part of the idea behind RAID5 -- uptime. A drive dies, the alarm goes off, you pull it from the machine's hotswap bay (like the Supermicro 5in3's Ockie favours), and slam a fresh new drive in. The raid starts rebuilding onto the new drive. All this swapping occurs with power flowing.

During all this, your users experience no downtime at all. Their data keeps on trucking, with them none the wiser as to the hard drive failure.
 
It took me about ten seconds to expand my zpool from a single mirrored pair to contain another mirrored pair as well, but that's kind of a special case :p ISTR when my brother took his from six to twelve disks it took about the same amount of time.
 
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