RAID Initializing

Posted on 2011-03-13
Last Modified: 2012-05-11
Question about RAID setups on Windows (embedded) with an Intel integrated controller (DP67BG). We have a system that must endure the occasional power outage (part of the implementation unfortunately) and we are not always afforded a graceful shutdown. The only raid level we have not tried is 10 but since it’s striped we assume a power outage will require it to rebuild/re-initialize.

Any ideas as to how we can have data redundancy and avoid rebuilds on power outages?  We can’t afford the performance hit.

Question by:suprdupr
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LVL 13

Expert Comment

ID: 35122718
Does the systemm have an UPS?

Author Comment

ID: 35122897
Yes but a tough fact of the implimentation is it is frequently moved with trade shows and the setup crews will often not shut down properly, and often disconnect the UPS.. we have no control over this, I wish we did.
LVL 13

Expert Comment

ID: 35122941
Ouch, that is a tough position.

No type of RAID or the OS for that matter is going to remain healthy being hard crashed repeatedly.

The Smart UPS line from APC allows you to have the system turned of at specific times, but I am guessing you do not have the luxury of knowing specific times that would work.
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LVL 47

Expert Comment

ID: 35123034
Actually above answer is incorrect. Some RAID controllers, such as HP SMARTArray & LSI's higher-end controllers have a built-in battery backup that preserves non-flushed data.  Just get one of those and you will be fine.  No performance penalty either.  There is enough RAM & battery power to protect you for an extended week-end.  Even if you are in middle of rebuild, you are covered.


Author Comment

ID: 35124520

At this point #3 seems reasonable, no reason to believe AustinComputerLabs comment was incorrect. dlethe comments are helpful and I am curious to know specifically, would the HP or LSI controllers NOT rebuild the drive array after a power outage.  Preserving the non-flushed data is great, but the end goal is to have the array not re-build after a power outage and reboot.

LVL 47

Accepted Solution

David earned 500 total points
ID: 35124616
If you have the right model of HP/LSI controller AND it is healthy AND the power-up was done before the battery discharged

Then unless it was in the middle of a rebuild before the power loss, then you will NOT need to do a rebuild.  That is because once power is restored, then even while the PC is booting, whatever I/Os in the queue will get copied to the disk as if power was never lost.   Hence, no need to rebuild, because there would be no corruption at the RAID.

However, there is another type of corruption, file-system corruption that you would get when you don't shut a computer down properly. Specifically if a volume was already mounted.  Then this is not RAID corruption, this is file system houskeeping.  So rebuilds would have to be done then.  

If the volume was dismounted before the power loss, then the cache BBU would be 100% effective as there would be no lost I/O. It never happened.

If volume was still open, then you would have to probably do a chkdsk, but that would be to check for problems with applications that were open and not anything to do with RAID-level corruption.
So answer is it depends ;)

(But the RAID BBU is highly effective at limiting the damage regardless, as the NTFS journals will be OK)

Author Comment

ID: 35126593
Thank you I will ask the admin to be sure to re-direct points.

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