I just bought a new hard drive, and I would like to use LVM on it. I created therefore a new physical volume with pvcreate
, accepting the default settings (which is probably the wisest thing to do).
As result, I've got my phiscal size all together, and no physical extent size, as shown by pvdisplay
:
PV Size 931.51 GiB
Allocatable yes
PE Size 0
After that I used vgcreate
to create my volume group. Again with default settings. What I obtained was not exactly what I expected, because of that 33.71 MiB
wasted:
PV Size 931.51 GiB / not usable 33.71 MiB
Allocatable yes
PE Size 4.00 MiB
By using the --units B
option ov pvdisplay
I was able to obtain the actual physical volume size, that is size = 1000204885504
bytes. Some fast calculations tell me that if we divide it by blocks of 4 MiB
we obtain...
size / (4 * mib)
238467.42761
With a wasted area of 1.71044 MiB
size - (4 * mib * 238467)
1793536
Which is much more reasonable.
I tried to create different sized volume groups by changing the -s
flag. Eventually I tried with 4 KiB
, obtained a 100% utilization of my physical volume:
PV Size 931.51 GiB / not usable 0
Allocatable yes
PE Size 4.00 KiB
So, my questions are:
Why did I get
33.71 MiB
flagged asnot usable
when the reasonable amount would have been1.71
?Is it advisable to maintain a very small physical extent size in order to minimize the wasted space? Is there any drawback in myI read on the Internet that a large physical extent size choicereduces the effects of external fragmentation. What is in your opinion a good compromise?
Thanks in advance for any kind answer.