[Veritas-vx] RAID-5 LOGGING

[Asiye Yigit]

Hello all;

Ýt is recommended to add raid-5 log device to the volume to recover the correct data in any case including system crash.

However, I am trying to understand how the data and parity changes are logged here? Do you know the structure of this area?

Data and parity itself couldn't write here, if it is like that those area should be big enough.

As far as i know, it is small area.

What kind of information for each data and parity changes is holdin here to re-paly the log?

Regards;

[Tony Griffiths]

Hi
The RAID5 log is used to recover from a double failure (Disk failure + sys crash). The RAID5 log is used to log all data and parity writes before committing them. Following a system crash the log will be replayed to the volume. There is a section in the admin guide:

https://sort.symantec.com/public/documents/sfha/5.1sp1/solaris/productguides/html/vxvm_admin/ch01s04s09s04.htm

Cheers
tony


From: veritas-vx-***@mailman.eng.auburn.edu [mailto:veritas-vx-***@mailman.eng.auburn.edu] On Behalf Of Asiye Yigit
Sent: 07 May 2011 17:07
To: veritas-***@mailman.eng.auburn.edu
Subject: [Veritas-vx] RAID-5 LOGGING

Hello all;
Ýt is recommended to add raid-5 log device to the volume to recover the correct data in any case including system crash.
However, I am trying to understand how the data and parity changes are logged here? Do you know the structure of this area?
Data and parity itself couldn't write here, if it is like that those area should be big enough.
As far as i know, it is small area.
What kind of information for each data and parity changes is holdin here to re-paly the log?
Regards;

[Asiye Yigit]

Hello;

I know this section. J

However, there is no further detail what kind of information is kept here according to what?

Best regards;





From: Tony Griffiths [mailto:***@symantec.com]
Sent: Monday, May 09, 2011 11:34 AM
To: Asiye Yigit; veritas-***@mailman.eng.auburn.edu
Subject: RE: RAID-5 LOGGING



Hi

The RAID5 log is used to recover from a double failure (Disk failure + sys crash). The RAID5 log is used to log all data and parity writes before committing them. Following a system crash the log will be replayed to the volume. There is a section in the admin guide:



https://sort.symantec.com/public/documents/sfha/5.1sp1/solaris/productguides/html/vxvm_admin/ch01s04s09s04.htm



Cheers

tony





From: veritas-vx-***@mailman.eng.auburn.edu [mailto:veritas-vx-***@mailman.eng.auburn.edu] On Behalf Of Asiye Yigit
Sent: 07 May 2011 17:07
To: veritas-***@mailman.eng.auburn.edu
Subject: [Veritas-vx] RAID-5 LOGGING



Hello all;

Ýt is recommended to add raid-5 log device to the volume to recover the correct data in any case including system crash.

However, I am trying to understand how the data and parity changes are logged here? Do you know the structure of this area?

Data and parity itself couldn't write here, if it is like that those area should be big enough.

As far as i know, it is small area.

What kind of information for each data and parity changes is holdin here to re-paly the log?

Regards;

[William Havey]

What kind of information is kept in the log? If the RAID5 volume is, for
example, 5 columns than 4 columns are data written by the application using
the volume, usually a file system and using the file system is the
application. So, what is in the RAID5 log is application data and the parity
stripe calculated from that data. Many sites will explain the XOR operation
to calculate parity.

You can not access a specific stripe in a volume. At best, you could, I
guess, use fsdb to examine the log content.

Bill

Post by Asiye Yigit
Hello;
I know this section. J
However, there is no further detail what kind of information is kept here
according to what?
Best regards;
*Sent:* Monday, May 09, 2011 11:34 AM
*Subject:* RE: RAID-5 LOGGING
Hi
The RAID5 log is used to recover from a double failure (Disk failure + sys
crash). The RAID5 log is used to log all data and parity writes before
committing them. Following a system crash the log will be replayed to the
https://sort.symantec.com/public/documents/sfha/5.1sp1/solaris/productguides/html/vxvm_admin/ch01s04s09s04.htm
Cheers
tony
*Sent:* 07 May 2011 17:07
*Subject:* [Veritas-vx] RAID-5 LOGGING
Hello all;
Ýt is recommended to add raid-5 log device to the volume to recover the
correct data in any case including system crash.
However, I am trying to understand how the data and parity changes are
logged here? Do you know the structure of this area?
Data and parity itself couldn't write here, if it is like that those area
should be big enough.
As far as i know, it is small area.
What kind of information for each data and parity changes is holdin here to
re-paly the log?
Regards;
_______________________________________________
http://mailman.eng.auburn.edu/mailman/listinfo/veritas-vx

[A Darren Dunham]

Post by Asiye Yigit
Hello all;
?t is recommended to add raid-5 log device to the volume to recover the correct data in any case including system crash.
However, I am trying to understand how the data and parity changes are logged here? Do you know the structure of this area?

Not the specifics. I believe it is basically an intent log for the R5
volume.

Post by Asiye Yigit
Data and parity itself couldn't write here, if it is like that those area should be big enough.

Correct. It is just temporary. Once all writes are committed, then the
data is not needed. So the log area can be quite small.

Post by Asiye Yigit
As far as i know, it is small area.
What kind of information for each data and parity changes is holdin
here to re-paly the log?

Presumably it is the full set of changes that will be made to the parity
stripe. I suppose it could be just the subset of changes on a
less-than-full-stripe write as well, but that gets into the nitty-gritty
details which I don't know about.

What level of information are you hoping for?