AutoRAID restore II

[Mike Fisher_5]

I read this thread with interest:
Dagmar: "AutoRAID restore"
http://forums.itrc.hp.com/cm/FamilyHome/1,,117!1!2,00.html

Just to expose my ignorance !!
It got me thinking about a a situation we've been asked about recently

If you have a remote site without I.T. skills
Where they may only get a I.T. skilled visit once a week

Is it possible to have the spare disc installed & recognised as a spare in the AutoRAID?

I have this notion that upon disc failure the AutoRAID would automatically do a restore to the spare
No need for the I.T. illiterate [such as me]
To have to put in the disc
No need to remove the failed one right then

I suppose I'm also asking about availability if an automatic restore were possible in the way I describe I can think of lots of reasons why this could be a recipe for disaster - just an idea though

Mike "humble mode" Fisher

[Bernhard Mueller · Accepted solution]

The Autoraid allows you to disable "AUTOINCLUDE"
then you could insert your *cold* spare
and when you need it you would manually INCLUDE this spare to allow for complete redundancy.

Though, this is not the way it was designed, I think it should work fine as long as you are willing to pay the extra disk.

Take into account that the AutoRaid can use disks of different sizes (up to 36GB)

Regards,
Bernhard

[Pete Randall]

Mike,

The AutoRAID has a "hot spare" capability. One (or more) of the disks are designated as "hot spares" and utilized as replacements in the event of a disk failure. To me, the key is that someone has to recognize that the failure has occurred, because you've still got to replace the faulty disk.


Pete

[Pete Randall]

Mike,

Actually, that last wasn't technically correct - AutoRAID doesn't reserve disk(s) for use as "hot spares", it reserves capacity "enough to rebuild the largest disk in the array. Until needed, the array uses the Active Hot Spare capacity as RAID 0/1 space to improve performance. The capacity for the Active Hot Spare is distributed across all the disks in the array." Quoting from the "HP Disk Array with AutoRAID User's Guide".


Pete

[Mike Fisher_5]

So
In a nutshell
Human intervention at the time will be required
Right?

[Pete Randall]

Mike,

Human intervention will be required. The idea behind the "hot spare" is that the intervention doesn't have to happen immediately. However, a second disk failure could lead to disaster so it's best to replace the failed disk as soon as possible.


Pete

[George_Dodds]

The performance will be reduced until the faulty disk is swapped out.

So i guess it depends whether your customer can work ok with the reduced performance until the disk is swapped.

I think ;)

Ta

George

[Eugeny Brychkov]

Just an idealistic example (some numbers may be incorrect :o) ): you own autoraid with 6x36GB disks, AHS turned on and you allocated only 50% of all available space.
What's AHS - active hot spare - is a space which is reserved in case of disk failure autoraid will be able to rebuild and there will be no 'permanent' (until failed drive will be replaced) redundancy loss.
Situation: autoraid loses one disk. Autoraid rebuilds data. After rebuild the layout as the following: AHS is still active, but you can create only LUN of size less than 36GB as you could before disk failed. Then autoraid is ready for next disk failure... etc.
Finally, when there will be no enough space to grab from 'free space' for rebuild AHS space will be used. Rebuild will complete successfully, but AHS will be disabled then. If then one more disk fail, then there will be NO AHS and NO space to rebuild, and array will be recovering using RAID algorithms (warning state). If then one more disk fails, then it's data loss
Eugeny

[Mike Fisher_5]

Eugeny

Very clear - you should be a teacher

[Eugeny Brychkov]

I was a teacher for 3 years... but such work is not so well payed here like in UK, Canada or US :o(
Eugeny