md + lvm + reiser
Excuse me if this has been covered already, though I did try to read through the archives. I am running md raid5 (software) over several drives and importing that into LVM and using reiserfs. It's worked fine for some time, but now I want to start snapshots. I've learned about the VFS lock patch, yes, but my real question is: why is the raid5 buffer cache constantly thrashing back and forth? I assume this has to do with a conflict between reiserfs's 4096 byte blocks and LVM's 512 SECTOR_SIZE. Or did I configure something wrong somewhere? Is it safe to just change SECTOR_SIZE in lvm.h or will that mess up on-disk structures? Thank you.
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chris jantzen kb7rnl =-> __O Insert witty comment here. _`\<,_ http://www.maybe.net/ (*)/ (*)
Quoted 10 lines · Chris Jantzen
Excuse me if this has been covered already, though I did try to read through the archives. I am running md raid5 (software) over several drives and importing that into LVM and using reiserfs. It's worked fine for some time, but now I want to start snapshots. I've learned about the VFS lock patch, yes, but my real question is: why is the raid5 buffer cache constantly thrashing back and forth? I assume this has to do with a conflict between reiserfs's 4096 byte blocks and LVM's 512
SECTOR_SIZE. Or did I configure something wrong somewhere? Is it safe to just changeSECTOR_SIZEinlvm.hor will that mess up on-disk structures? Thank you.
I have exactly the same symptoms with the same configuration (md + lvm + reiser) ; the raid5 cache size keeps changing when I start using snapshots. Does someone have some tips to avoid/explain this ?
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[ Xavier Montagutelli `""' ] [ INSA Toulouse 0--0 ] [ ---------oOOo---()---oOOo---------- ] [ Dpt de Math / Service Informatique Tel: +33 5 61 55 93 38 / 67 ] [ 135, Avenue de Rangueil Fax: +33 5 61 55 93 20 / 60 ] [ 31077 Toulouse Cedex 4 Mel: [email protected] ]
Quoted 4 lines · Xavier Montagutelli
Quoted 2 lines · Chris Jantzen
VFS lock patch, yes, but my real question is: why is the raid5 buffer cache constantly thrashing back and forth? I assume this has to do with
...
Quoted 3 lines
I have exactly the same symptoms with the same configuration (md + lvm + reiser) ; the raid5 cache size keeps changing when I start using snapshots. Does someone have some tips to avoid/explain this ?
The r5 cache needs a fixed request size, Neil once explained me, but i do not recall the exact details now, when the md layer receives a request with different size, it has to be emptied and recreated with the new size.
This is the meaning of the message, it is harmless, except for performance, at the moment the best that can be done about it is commenting out the message.
regards,
L.
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Luca Berra -- [email protected] Communication Media & Services S.r.l. /"\ \ / ASCII RIBBON CAMPAIGN X AGAINST HTML MAIL / \
Quoted 10 lines · Luca Berra
Quoted 4 lines · Xavier Montagutelli
Quoted 2 lines · Chris Jantzen
VFS lock patch, yes, but my real question is: why is the raid5 buffer cache constantly thrashing back and forth? I assume this has to do with
...
Quoted 3 lines
I have exactly the same symptoms with the same configuration (md + lvm + reiser) ; the raid5 cache size keeps changing when I start using snapshots. Does someone have some tips to avoid/explain this ?
Quoted 7 lines
The r5 cache needs a fixed request size, Neil once explained me, but i do not recall the exact details now, when the md layer receives a request with different size, it has to be emptied and recreated with the new size.
This is the meaning of the message, it is harmless, except for performance, at the moment the best that can be done about it is commenting out the message.
Well, I know it's harmful and I know that's exactly why it happens. I want my performance though! :-) I was wondering if any of the deep LVM guru's could say whether SECTOR_SIZE could be safely bumped up. Thanks for the input and I think I'll wait a few more days before making a hard decision.
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chris jantzen kb7rnl =-> __O Insert witty comment here. _`\<,_ http://www.maybe.net/ (*)/ (*)