AS-608T Query

[inoran81]

Hi there,

I just purchased the AS-608T NAS and i must say that it rocks!

One query i have encountered along the way.

In the ADM menu, under -> Storage Manager -> Volume -> Data Protection it states "Good (Faulty Disk Allowed : 1)" However during my initializing stage, i remember seeing two faulty disk allowed when i chosed RAID10. In theory RAID 10 promise up to two disks failure too, so i'm not sure is its a firmware glitch or an issue from my side. All of my 8 disks are in a active and healthy status too.

Below is an illustration of my scenario :



Hope to get some remedy on this, thanks.

Happy lunar new year to those that lived in Taiwan or Chinese countries!

[JohnnyFive]

Well the right answer would be: it depends on the drive that fails....
I'm afraid they are right with their one drive failure in a 4 drive situation. this is because it just depends on which drives fails after the first one, if the set is still alive or not.
please have a look at the picture below:



you see four drives. lets number them from left to right, 1 to 4. your data is striped (raid 0) over two raid-1 sets (drive 1+2 and 3+4)

if drive 1 fails, you can't have drive 2 to fail also, without losing the whole raidset. But you could loose drive 3 or 4 e.g. So depending on the situation a four drive raid-10 config could either loose 1 or 2 drives.

for more background information, please have a look at: http://en.wikipedia.org/wiki/RAID_10#RAID_0.2B1

Redundancy and data-loss recovery capability
All but one drive from each RAID 1 set could fail without damaging the data. However, if the failed drive is not replaced, the single working hard drive in the set then becomes a single point of failure for the entire array. If that single hard drive then fails, all data stored in the entire array is lost. As is the case with RAID 0+1, if a failed drive is not replaced in a RAID 10 configuration then a single uncorrectable media error occurring on the mirrored hard drive would result in data loss. Some RAID 10 vendors address this problem by supporting a "hot spare" drive, which automatically replaces and rebuilds a failed drive in the array.

[ddaniel51]

Raid 6 will tolerate 2 drive faults. I currently have 6 drives in a raid 6 and one in service as a hot spare. The number 7 slot holds a cold spare so I don't misplace it or use it in something else by mistake.

[inoran81]

Well the right answer would be: it depends on the drive that fails....
I'm afraid they are right with their one drive failure in a 4 drive situation. this is because it just depends on which drives fails after the first one, if the set is still alive or not.
please have a look at the picture below:

you see four drives. lets number them from left to right, 1 to 4. your data is striped (raid 0) over two raid-1 sets (drive 1+2 and 3+4)

if drive 1 fails, you can't have drive 2 to fail also, without losing the whole raidset. But you could loose drive 3 or 4 e.g. So depending on the situation a four drive raid-10 config could either loose 1 or 2 drives.

for more background information, please have a look at: http://en.wikipedia.org/wiki/RAID_10#RAID_0.2B1

Redundancy and data-loss recovery capability
All but one drive from each RAID 1 set could fail without damaging the data. However, if the failed drive is not replaced, the single working hard drive in the set then becomes a single point of failure for the entire array. If that single hard drive then fails, all data stored in the entire array is lost. As is the case with RAID 0+1, if a failed drive is not replaced in a RAID 10 configuration then a single uncorrectable media error occurring on the mirrored hard drive would result in data loss. Some RAID 10 vendors address this problem by supporting a "hot spare" drive, which automatically replaces and rebuilds a failed drive in the array.

I get it now... thanks so much for your explanation and illustration. i reckon i understand how it works now...

[inoran81]

Raid 6 will tolerate 2 drive faults. I currently have 6 drives in a raid 6 and one in service as a hot spare. The number 7 slot holds a cold spare so I don't misplace it or use it in something else by mistake.

In a RAID 10 scenario - how many hot/cold spare can i assign my disks to? If all my 8 disks are now part of the volume, do i need to "break" them up to assign the spare disk? what benefits will i get from those spare disk(s) even though my redundancy is already in place with RAID 10.

Kindly advice, thanks bud!

[James.W@AST]

Hi inoran81,

Since you have all 8 drives in one volume (RAID10), therefore, if you wanna assign a (hot) spare drive to this volume, then you will need to "break" it first, otherwise you won't have any extra drive as the spare drive. The most useful benefit of an hot spare drive is that when any of the hard drives (within RAID volume) is dead/missing, the hot spare drive will replace the dead/missing one automatically, and this lowers the risk of losing any data.

I personally think RAID10 already provides enough redundancy, you can simply set up the alert e-mail notification. Once there's something with any of the drives, you will be notified right away and you should still have enough time to replace it by yourself.

JW