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[linux-lvm] Some questions after starting to use 1.1-rc1



I've been using 0.9.1_beta6 for ages, and just upgraded to 1.1-rc1
(I like "-qn" and the fact that minor device numbers are static!)

1) I've been comparing the speed of LVM over RAID0 with striped LVM, using:
	perl -e '$n=1900;$x="X"x(1024*1024);foreach $i(1..$n){print $x}'
   and I find that striped LVM takes 50% longer.
   Due to the different areas on the physical disk, there should be some
   difference (hdparm shows 37MB/s vs 31MB/s) and the stride might effect
   things, but vmstat shows that with striped LVM there is a period of disk
   IO, then no disk IO at the end (sample at end of email).  Any ideas why ?

2) When I tried to extend the striped partition, it failed when it used up the
   first two PVs, and will not start the next two.  Ideas ?

#  lvextend -L+1 /dev/vg97/test
lvextend -- rounding relative size up to physical extent boundary
lvextend -- rounding size to stripe boundary size
lvextend -- extending logical volume "/dev/vg97/test" to 2 GB
lvextend -- not enough free/allocatable physical extents to extend logical 
volume "/dev/vg97/test"

# pvscan
...
pvscan -- ACTIVE   PV "/dev/.../part26" of VG "vg97" [1020 MB / 0 free]
pvscan -- ACTIVE   PV "/dev/.../part27" of VG "vg97" [1020 MB / 1020 MB free]
pvscan -- ACTIVE   PV "/dev/.../part26" of VG "vg97" [1020 MB / 0 free]
pvscan -- ACTIVE   PV "/dev/.../part27" of VG "vg97" [1020 MB / 1020 MB free]
pvscan -- total: 24 [39.13 GB] / in use: 24 [39.13 GB] / in no VG: 0 [0]

#

3) When trying out the new "-qn" (rah rah!) I wanted to tell the system
	forget about vg99; stop one PV; vgscan
   to see how it got on with a missing PV.  The only way I could think of to
   say "forget vg99" was to vgexport it. Stopped one RAID array, and vgscan
   found vg99 (no need for "-qn" as I remember). Great ! restarted the array.
   However, I could not the "forget" about vg99 again to allow me to add the
   PV back again, as when I tried to export it, it said it was already
   exported (I assume because it saw the array which I had restarted ...
   a) Is there a better way to say "forget about vg99" ?
	(e.g. "vgremove --leave-all-data-ASIS /dev/vg99")
   b) should it be possible to export a VG if there is a PV of that VG which
      is still exported ?

4) http://www.sistina.com/lvm_howtos/lvm_howto/Recovery_when_things_go_w.html
   (etc) are empty apart from:
	This is just stuff from the end of Joe's new LVM HowTo draft that I
	didn't know where to put. It should get moved to separate files as
	content is added 
  but there is no "stuff" :-((   Where is "Joe's" HowTo ?

5) is there some utility to display the contents of VGDA on disk, /etc/lvm*,
   etc;  show where the first PE is in a PV, etc ?


vmstat output:

   procs                    memory    swap          io     system         cpu
 r  b  w swpd   free   buff  cache  si  so    bi    bo   in    cs  us  sy  id
 1  0  0    0 1658156   6640 323648   0   0     0     0  135    53   0  50  50
 1  0  1    0 1488868   6640 464556   0   0     0 60832  751    42   0  84  16
 1  0  1    0 1394820   6640 553644   0   0     0 53640  872    37   0  82  18
 1  0  1    0 1325356   6640 631468   0   0     0 43532  935    32   1  78  21
 2  0  1    0 1269744   6640 689836   0   0     0 54848 1095    31   0 100   0
 1  0  1    0 1192132   6640 759468   0   0     0 59680  925    32   0 100   0
 2  0  1    0 1163724   6640 808620   0   0     0 44600 1139    31   0 100   0
 1  0  1    0 1125648   6640 854700   0   0     0 55364 1625    35   1  99   0
 1  0  1    0 1085020   6640 896684   0   0     0 60380 2188    31   0 100   0
 1  0  1    0 956880   6640  975532   0   0     0 91424 1639    30   0 100   0
 1  0  1    0 885072   6640 1061548   0   0     0 36624  916    34   1  77  22
 1  0  1    0 870856   6640 1104556   0   0     0 38384 1169    31   0  99   0
 1  0  1    0 762148   6640 1190692   0   0     0 69908  873    31   0  93   7
 1  0  1    0 711120   6640 1259180   0   0     0 37896 1331    32   1  87  12
 2  0  1    0 655180   6640 1315500   0   0     0 57808 1356    34   1  99   0
 1  0  1    0 576164   6640 1381036   0   0     0 67068 1261    33   0 100   0
 2  0  1    0 557596   6640 1423020   0   0     0 43252 1170    29   1  99   0
 2  0  1    0 444896   6640 1500144   0   0     0 82376 1372    34   0 100   0
 1  0  1    0 411028   6640 1549996   0   0     0 45384 1112    33   0 100   0
 1  0  1    0 359984   6640 1604268   0   0     0 55176 1157    33   2  97   1
 1  0  1    0 322548   6640 1654276   0   0     0 90664 1264    35   0  95   5
 1  0  1    0 256308   6640 1725492   0   0     0 68960 1147    35   0  56  43
 1  0  1    0 168056   6640 1813744   0   0     0 42748  941   139   0  49  51
 1  0  1    0 108168   6640 1873632   0   0     0 76124 1120   126   0  51  49
 0  1  1    0  35012   6640 1946788   0   0     0 45216  928   174   0  46  54
 1  0  1    0  17240   6640 1964560   0   0     0 52916 1183   315   0  51  49
 1  0  1    0  17244   6640 1964556   0   0     0 67456 1149    34   0  56  44
 1  0  0    0  17244   6640 1964556   0   0     0 59724  838    36   0  54  46
 1  0  0    0  17244   6640 1964556   0   0     0     0  767    31   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  112    31   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  117    31   0  51  49
 1  0  0    0  17244   6640 1964556   0   0     0     0  115    30   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  109    33   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  116    31   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  109    30   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  110    33   0  51  49
 1  0  0    0  17244   6640 1964556   0   0     0     0  111    31   0  50  50
 1  0  0    0  17244   6640 1964556   0   0     0     0  115    31   0  50  50
 1  0  0    0  17240   6640 1964560   0   0     0     0  114    32   0  50  50
 1  0  0    0  17240   6640 1964560   0   0     0     0  116    31   0  51  49
 1  0  0    0  17240   6640 1964560   0   0     0     0  114    32   0  52  48
 1  0  0    0  17240   6640 1964560   0   0     0     0  116    31   0  50  50
 1  0  1    0  50584   6640 1933328   0   0     0     0  124    43   0  53  46




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