paul at clubi.ie, Fri, Jun 01, 2007 at 09:41:35PM +0100:
> >Not in case of AIX's LVM.
> Care to explain?
In AIX mirroring is part of LVM which, by the way, isn't optional. AIX
comes with LVM, period. An AIX machine has at least a volume group,
named rootvg, where a number of logical volumes are defined for fixed
mountpoints: /dev/hd6 is the paging space, /dev/hd5 is the boot volume,
hd4 is /, hd2 is /usr, hd3 /tmp, hd1 /home, and lastly /dev/hd9var (sic) is /var.
This is of course the basic set, you can add LVs in the rootvg, and more VGs, and mount
them where you like it best.
One of the features of AIX LVM is mirroring, called "adding more copies
to a VG/LV", to a maximum of 2 (for a total of 3 copies, double
redundancy). Copies can be added in strict policy (id est, sector-by-sector),
or non-strictly (just copying the data wherever can be done on the other
disks). So, mirroring and data-consistency *is* an LVM feature in case
of AIX's LVM. RAID5 isn't supported - just (double) mirroring.
Furthermore, you can define per-LV physical allocation policy on the
disk - you can approximate this behaviour in Linux by defining more
partitions in different positions on the disks and then defining them as
separate PVs, add them to the same VG and then span LVs over them, but
it's tricky. And unuseful, given today disks' performance levels.
By the way, the maximum volume size in a JFS volume is 4 petabytes IIRC.
Don't know for JFS2, but hasn't been ported to Linux (yet, AFAIK).
Which is slightly OT given this ain't IAUG... :D
pbm - "But something happened - don't know if I can explain it
just call me the man whose heart turned to stone"
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