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Can Raid detect bad sector?

Posted on 2002-05-13
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Last Modified: 2008-02-01
Hi,

I am using PERC 3/SC and running RAID 1, i have the following question:

1. Can PERC 3/SC detect bad sector?  If yes, what action it takes?  If no, should i have to check the disk occasionally?

2. i have turned down a disk and rebuild it, but i have abort the rebuilding process and turn it ONLINE and reboot.  However, during reboot, it just say it can't detect the bootable disk even i have turned the orginal disk to offline state.  So is that means i can't abort the rebuilding state and put it online?  But why it makes my original disk also non-bootable?

3. There must have a time gap between the rebuilding and put the disk online, so what happend if some are writing data on the disk?  Can PERC 3/SC put the data on BOTH disks? OR any good suggestion?

4. PERC 3/SC provides a data checking function.  But when should i use it?  Use it when the disk has problem or check it occasionally?

Thanks a lot!

regards
dp
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Question by:d_p2
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13 Comments
 
LVL 7

Expert Comment

by:frache
ID: 7007907
Can you give more details about context ( PC,server ...,OS ...)

1) Bads sectors are detected/managed by "internal" disk controller (electonic card on your disk).

2) Never reboot a PC or a server when you rebuild a disk ... you "lock" your disks or you loose your data ...


You can try to erase everything with a "0" program on your mirror disk and after try to rebuild it ...

You can try also to reboot with your "good" disk ( dismount mirror disk), backup data and after reinstall everything and restore data ...


3) "Rebuild" disk if the perfect copy of your "good" disk when rebuild process is finish.
You can use Pc or server during rebuild ... no data gap at the end of rebuild process.

4) When a disk has a problem ...
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LVL 7

Expert Comment

by:frache
ID: 7008508
You must read :

1) (electronic card on your disk).

3) "Rebuild" disk IS the perfect copy of your "good" disk when rebuild process is finish.
----------
Do you have a PowerEdge Dell server ? which model ?
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Author Comment

by:d_p2
ID: 7008698
yes, i am using PowerEdge 1400SC.
0
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LVL 7

Expert Comment

by:frache
ID: 7008798

4) More details from Dell site :

This function checks mirror synchronization and rebuilds parity if necessary. You also use this function if your disk is in a degraded state. Running Check Consistency may be able to restore your disk to Ready status.

To check consistency and restore redundancy:
Right-click the virtual disk to be checked.


Click Check Consistency.


The Check Consistency operation displays progress information in the right pane. To view the progress, click the parent of the virtual disk. The status of the virtual disk will be Resynching, and progress information will display until the operation is finished.

My link : http://docs.us.dell.com/docs/software/smarrman/marb312/ch8_perc.htm

-----------

I have a large experience with Compaq SmartArray raid controller.
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LVL 7

Expert Comment

by:frache
ID: 7008801
3)


During a rebuild, the complete contents of an array disk are reconstructed. A rebuild operation can take place during normal operation, but it will degrade performance.

The rebuild rate is the fraction of the compute cycles dedicated to rebuilding failed array disks. The PERC 2/SC, 2/DC, 3/SC, 3/DCL, 3/DC, 3/QC, and CERC ATA100/4ch controller rebuild rate can be configured between 0% and 100%. At 0%, the rebuild is done only if the system is not doing anything else. At 100%, the rebuild has a higher priority than any other system activity; the system is totally dedicated to rebuilding the failed array disks.

You can reduce the rebuild rate to maintain system performance during the rebuild operation. However, a reduced rebuild rate extends the rebuild time.

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LVL 7

Expert Comment

by:frache
ID: 7008826
2)

About your problem :
Perhaps your array disk has been set to offline.

Try to boot your server with your "Dell Open Manage Cd" and verify the array state with Array Manager. This tool have a command "online".

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LVL 7

Expert Comment

by:frache
ID: 7009684
1) About bad sector :
If you want alert about harddisk, you can use SMNP tools probably given with your server.
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Author Comment

by:d_p2
ID: 7010676
Thanks frache

1) OK, i will use SMNP

2) No, i am sure both disks are set to ONLINE and i have insert the linux's installation disk. It can't locate the partitions.

3) yup, i know there may have a performance problem if i rebuild it in the normal operation.  However, can it synchronize the data even the disk is in READY state?

Thanks a lot!

regards,
dp


0
 
LVL 7

Expert Comment

by:frache
ID: 7013107



3) if you broke a mirror ( disk out of order / remove one disk ), when you plug a new disk , rebuild process is automatic. It's a "hardware" process without operator control.
If you STOP operation during rebuild, you loose your data or you lock your disks ... it's depend ...

"yup, i know there may have a performance problem if i rebuild it in the normal operation."
-> no, because rebuid can take several hours  ...
 
2 )
Do you know "good" disk (disk with data)?

Try that :

Unplug second disk ...

Set controller to raid 0 ... if you have an advertissement
about loss of data ... STOP ...
OR
Erase raid configuration ... ( controller CMOS)

Try to boot ... raid controller look for data on harddisk

If you can boot, make a backup...

Erase raid configuration ... ( controller CMOS) and erase all disks

Create array (raid1)

Install ...

Restore ...



Note : Don't try to read data with an ordinary scsi controller ... it doesn't work ...


0
 

Author Comment

by:d_p2
ID: 7015859
3)
""yup, i know there may have a performance problem if i rebuild it in the normal operation."
-> no, because rebuid can take several hours  ..."
=>Rebuild can take several hours or longer as it depends on the rebuild rate and you can adjust the rebuild rate. If rebuild rate is 100%, rebuild process is the highest priority job.  But the default setting is 30% which means other higher priority jobs can still be performed.  Therefore my question is if other higher priority job which write data to the disk (health disk), will it also write to the rebuilding disk?

1)Just curious, can the PERC 3/SC detect the bad sector?  if yes, what it will do?  

Thank you very much and much appreciate your help!

regards,
dp
0
 
LVL 7

Accepted Solution

by:
frache earned 1000 total points
ID: 7016034


1) You can find/detect bad sectors with a specific software.
3 ways :
- a diagnostic tools (look in Dell toolkit)
- some SCSI controllers (Adaptec) have this capability built into the controller's BIOS. You can usually find this under "Disk Utilities."
- O.S : scandisk for example ...


3) When controller rebuilds data on the second disk, another new data can be added to the health disk. At the end of the rebuilding process ALL data ( old and new) are present on each disk.

Process ?
New datas are added in a "hole" (area without data)or at the end of data in the health disk.
2 ways possible :
controller stops copy and it writes data in two disks
or
data are written at the end of the data in the health disk, and after the rebuilding  process copies the data (5 min later for example).
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LVL 1

Expert Comment

by:Moondancer
ID: 7016699
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Author Comment

by:d_p2
ID: 7019222
frache,

Thanks a lot and much appreciate for your help!

regards,
dp
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