Configuring boot partition with LVM
Quoted 6 lines · Christopher Shaulis
I can't remember exactly how they explained it, but IBM has a good reason for not allowing mirrored dump devices. I think the idea is that in order to catch the system dumping in the LVM code itself, you have to write the dump without the aid of the LVM. I think the way that works is that it precomputes a list of offset:extent lists for the device when it is brought online.
I think that the issue isn't when the dump is written to a mirrored LV (as the dump will only go to one or the other copy of the LV), but when it is read back there is no way to determine which copy you will read from (I/O load balancing causes reads to come from either PV), so you may get intermittent garbage inside the dump...
Cheers, Andreas
Signature · 3 lines
Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
\ would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- DogbertQuoted 7 lines · Andreas Dilger
Quoted 6 lines · Christopher Shaulis
I can't remember exactly how they explained it, but IBM has a good reason for not allowing mirrored dump devices. I think the idea is that in order to catch the system dumping in the LVM code itself, you have to write the dump without the aid of the LVM. I think the way that works is that it precomputes a list of offset:extent lists for the device when it is brought online.
Dunno 'bout IBM, with HP you can setup dump to a mirrored LV, but it will dump only on the first PV, this is due to dumping being handled by the firmware, which knows nothing about LVM
dump LVs must be contiguous on disk, but you can have many of them
Quoted 5 lines
I think that the issue isn't when the dump is written to a mirrored LV (as the dump will only go to one or the other copy of the LV), but when it is read back there is no way to determine which copy you will read from (I/O load balancing causes reads to come from either PV), so you may get intermittent garbage inside the dump...
This is one issue, another nice pitfall is that dump is usually read from disk after mirror reconstruction has begun (remember, if it crashed mirror copies aren't synchronized), so you may not exactly found what you expect in the dump :)
With HP you must specify a couple of options in lv creation to disable mirror reconstruction.
L.
Signature · 2 lines
Luca Berra -- [email protected] Communication Media & Services S.r.l.