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Background parity initialization

 
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Occasional Contributor

Background parity initialization

Hello eveybody

It's my first time with Raid 50 

I've created a Raid 50 using 10 X 300G SAS HDD on DL 380 G10 with p408 controller. I found there is a message which says: 

Background parity initialization is in progress : 10% and ... . 

- Can I turn server off during this procedure and start it in another time? Or it should be complete before eveyting?

- Is it a ONE TIME process or it will repeat with any drive replacement ?

- If the answer of second question is YES, does it take a long while or cause any performance issue? I read that DELL servers don't show us new drive space before background parity initialization done . What about HPE servers? 

I thought a parity initialization with new arraived disks without any data will be complete in a few seconds! How long does it take ?

3 REPLIES 3
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Visitor

Re: Background parity initialization

Hello Salemmahara,

Here is what I can tell you:

1.Can I turn server off during this procedure and start it in another time? Or it should be complete before eveyting?


         If the server is powered off during the process it will pause and continue when the server is back on.

2. Is it a ONE TIME process or it will repeat with any drive replacement ?


        When a drive is replaced (or even plugged out for some reason) a rebuild proccess will be initated and the parity will be calculated/initializaed once again. In short, yes, it will go thorugh the process with every drive replacement, however it might not be as lengty as the first time.

3.If the answer of second question is YES, does it take a long while or cause any performance issue? I read that DELL servers don't show us new drive space before background parity initialization done . What about HPE servers?


       With a RAID 50 of this size the process can take a long time (days, even weeks) as by default the process is set to priority "Delay" which means that the process will run only when the controller is inactive for more than 15 seconds and pause when any activity is detected.
During the innitial parity initialization process the RAID is protected from single drive failure so I would advise you to let the process finish before activly using the server/controller.
To speed up the process you can try and leave the controller innactive until the process is finished as well as set the "Surface Scan Analysis Priority" to high temporarily, until the process is complete, then switch it back to medium where it should have innitially been.
The process does affect performance somewhat and I would advise that you wait it out before using the controller/server heavily.

So to recap:
1. If you turn the server off the process is paused.
2.The process is initated with every drive replacement as it rebuilds.
3.If the controller is used while the process is running it can take a long time. The process does somewhat affect performance. You should let the process finish before healivy using the controller as one one drive failure is allowed. To speed up the process you can leave the controller inactive and set the "Surface Scan Analysis Priority" to high until the process is finished and set it back to the default value after (medium).

I hope this answers all of your question and you find it helpful.

Best regards,
Ivan

I am an HPE Employee
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Regular Advisor

Re: Background parity initialization

Hi @IvBuh ,

Thank you for the reply and for answering right on-point!

That was a very clear answer on an issue that I feel there's so much confusion about out there. If I may follow up with a question in a context of a less sophisticated smart array configuration - good old RAID5. (4 disks, 3 usable total capacity).

Once a drive is replaced it takes an hour or so to rebuild the array. Then HPE indicates that one is "out of the woods" so to speak by the red alerts clearing automatically. However after the array rebuild is complete the next step in the process is background parity initialization, which as you explained can take quite a long time to finish.

My question is exactly during Background parity initialization - is RAID5 protected from a single drive failure or is it not while Background parity initialization is running?

Thank you

~B

Highlighted
Visitor

Re: Background parity initialization

Hi Boyan,

I am happy my answer was helpful

As for the new questions, the answer is yes and no.

  • Yes, the drive is safe as the main data is written to the new drive and the drive is now in use.
  • No, because any new data that has been written on the drive will be lost if it fails, but that is only the small amount of extra data on the array that has been added post readding the new drive to the RAID and is currently being calculated (indicated by the background parity initialization). This process runs frequently on the controller as new data is written to the array as it need to calculate new parity data for the new "real" data that's being added. The process runs in the background as not to hinder the controller performance especially during intensive read/write cycles. 

So in term the new drive is safe as the old data is backed up, however any new data (small amounts) is in danger while the new parity is being innitilized, however this goes for any new data and not only in case a drive is replaced.

Let me know if you have any further questions.

Best Regards,

Ivan

I am an HPE Employee