| 1 |
LVM 1.0.8
|
| 2 |
$Date: 2003/11/17 15:58:54 $
|
| 3 |
Logical Volume Manager frequently asked questions:
|
| 4 |
--------------------------------------------------
|
| 5 |
|
| 6 |
Q0: Where can I find more information about the
|
| 7 |
Logical Volume Manager for Linux?
|
| 8 |
|
| 9 |
A0: Please see <http://www.sistina.com/lvm> and/or join
|
| 10 |
our mailing list at <Linux-LVM@sistina.com> by following the subscription
|
| 11 |
instructions at <http://www.sistina.com/lvm>.
|
| 12 |
You can find pointers to LVM howtos on the Web there as well.
|
| 13 |
|
| 14 |
|
| 15 |
|
| 16 |
Q1: Why can't I create my volume group "mygroup"?
|
| 17 |
|
| 18 |
A1: You can't create a volume group with the same name as an existing one.
|
| 19 |
You can't create more than 99 volume groups at the moment.
|
| 20 |
You are only able to use inititalized physical volumes (see pvcreate(8)).
|
| 21 |
|
| 22 |
|
| 23 |
|
| 24 |
Q2: Why can't I create a physical volume with pvcreate(8)?
|
| 25 |
|
| 26 |
A2: Maybe pvcreate(8) complains that the physical volume has already
|
| 27 |
been initialized. So... think about "pvcreate -f[f] ...".
|
| 28 |
But DON'T DO THAT, if the physical volume belongs to another volume group!
|
| 29 |
Remember to set the partition system id to 0x8e with fdisk(8) before
|
| 30 |
trying pvcreate(8) on it.
|
| 31 |
|
| 32 |
|
| 33 |
|
| 34 |
Q3: Why am I not able to extend a logical volume?
|
| 35 |
|
| 36 |
A3: Your volume group is full or you've already reached the maximum
|
| 37 |
logical volume size in that volume group. Logical volume size is limited
|
| 38 |
by the size of the physical extents times their maximum amount, which
|
| 39 |
only can be set at volume group creation time.
|
| 40 |
The default physical extent size is 4MB which limits ;-) logical
|
| 41 |
volumes to a maximum of 256 Gigabyte (see vgcreate(8), vgdisplay(8)).
|
| 42 |
If your volume group isn't full or you didn't reach the current
|
| 43 |
logical volume size limit, your logical volume may have striped
|
| 44 |
or contiguous allocation policy. Have a look at the physical volumes
|
| 45 |
with vgdisplay or pvdisplay(8) to figure out, if there are not enough
|
| 46 |
free (contiguous) physical extents.
|
| 47 |
|
| 48 |
|
| 49 |
|
| 50 |
Q4: Why can't I move my logical volume(s) away from a physical
|
| 51 |
volume with pvmove(8).
|
| 52 |
|
| 53 |
A4: Look at the free space on all destination disks you want to use
|
| 54 |
(or which are implicitly used) AND at the attributes of the logical
|
| 55 |
volumes to be moved.
|
| 56 |
Remember: you can't move a contiguous logical volume when there isn't
|
| 57 |
enough free contiguous space on any destination disk.
|
| 58 |
In this case you can think about changing from contiguous
|
| 59 |
allocation policy to next free and do the attribute change
|
| 60 |
with lvchange(8).
|
| 61 |
You can't move a striped logical volume either, if there isn't
|
| 62 |
enough space for the complete stripe on any destination
|
| 63 |
physical volume.
|
| 64 |
You can't move to physical volumes which are NOT allocatable.
|
| 65 |
Think about changing this with pvchange(8).
|
| 66 |
|
| 67 |
|
| 68 |
|
| 69 |
Q5: My striped logical volume works horrible slowly,
|
| 70 |
what's going on?
|
| 71 |
|
| 72 |
A5: If you put it on two or more physical volumes based on partitions on
|
| 73 |
one disk, you will not gain any performance.
|
| 74 |
Remember: you are allowed to use two or more partitions of one disk as
|
| 75 |
physical volumes (this only makes sense for next free
|
| 76 |
allocated logical volumes on those physical volumes).
|
| 77 |
If you have attached two IDE disks to one adapter, you can't
|
| 78 |
get parallel i/o on these two disks.
|
| 79 |
|
| 80 |
|
| 81 |
|
| 82 |
Q6: Why can I not rename my volume group / logical volume?
|
| 83 |
|
| 84 |
A6: You have to deactivate them before you are allowed to rename them
|
| 85 |
(see lvrename(8), vgrename(8)).
|
| 86 |
|
| 87 |
|
| 88 |
|
| 89 |
Q7: The LVM kernel patch in the LVM distribution is not compatible
|
| 90 |
with my Linux version.
|
| 91 |
Where's help?
|
| 92 |
|
| 93 |
A7: If this relly is the case after following the instructions
|
| 94 |
contained in PATCHES/README please send an email to <linux-lvm@sistina.com>.
|
| 95 |
|
| 96 |
|
| 97 |
Q8: A LVM command was just working when my system crashed...
|
| 98 |
Help please!?
|
| 99 |
|
| 100 |
A8: Bring your system back online and look at the volume group
|
| 101 |
backup files in /etc/lvmconf.
|
| 102 |
There's at least one called /etc/lvmconf/VolumeGroupName.conf and
|
| 103 |
possible more in the backup history called
|
| 104 |
/etc/lvmconf/VolumeGroupName.conf.*.old.
|
| 105 |
You can use these backup files to bring the configuration
|
| 106 |
back to the one before the crash (see vgcfgrestore(8)).
|
| 107 |
|
| 108 |
|
| 109 |
|
| 110 |
Q9: Why are my logical volumes limited to 256 GB in size?
|
| 111 |
|
| 112 |
A9: This is NOT an absolute limit but it depends on the physical extent size you
|
| 113 |
configured at volume group creation time.
|
| 114 |
Please use option -s of the vgcreate command to give a larger physical
|
| 115 |
extent size. For example with a physical extent size of 524288 KB (512 MB)
|
| 116 |
you are able to map a logical volume of 32 Terabyte. Remember that actual
|
| 117 |
32 bit kernels are limited to 2 Terabytes (with 512 byte block size).
|
| 118 |
|
| 119 |
|
| 120 |
|
| 121 |
Q10: Why can't I split my volume group my_vg?
|
| 122 |
|
| 123 |
A10: The physical volumes you want to split into another volume group
|
| 124 |
may NOT have logical extents of logical volumes belonging to the original
|
| 125 |
volume group you started with. Please use pvmove to seperate
|
| 126 |
the logical volumes.
|
| 127 |
|
| 128 |
|
| 129 |
|
| 130 |
Q11: Why can't I merge my two volume groups my_vg1 and my_vg2?
|
| 131 |
|
| 132 |
A11: A merged volume group can't go beyond the physical or logical volume
|
| 133 |
limits of the destination volume group. This means for eg. that you
|
| 134 |
can't merge my_vg1 with 20 logical volumes and my_vg2 with 30 logical
|
| 135 |
volumes getting my_vg1, if my_vg1 has a 31 logical volume limit.
|
| 136 |
You are only able to merge (currently) volume groups with equal
|
| 137 |
physical extent sizes.
|
| 138 |
|
| 139 |
|
| 140 |
|
| 141 |
Q12: How can I move parts of my logical volume with very intensive I/O
|
| 142 |
to a different physical volume?
|
| 143 |
|
| 144 |
A12: Please look at pvmove(8) and use the logical extent syntax to do the job.
|
| 145 |
|
| 146 |
|
| 147 |
Q13: I have a compile problem and/or a runtime problem with the LVM.
|
| 148 |
Where to ask for help?
|
| 149 |
|
| 150 |
A13: Please send me a bug mail request to
|
| 151 |
<Linux-LVM-Bug@Sistina.com> or
|
| 152 |
to the linux-lvm mailing list.
|
| 153 |
|
| 154 |
|
| 155 |
Q14: Where can I ask for a missing feature or for a better way to implement
|
| 156 |
something in the LVM?
|
| 157 |
|
| 158 |
A14: Please send me an enhancement mail request
|
| 159 |
to <Linux-LVM-Enhancement@Sistina.com> or
|
| 160 |
to the linux-lvm mailing list.
|
| 161 |
|
| 162 |
|
| 163 |
Q15: Why is LVM not in the stock kernel?
|
| 164 |
|
| 165 |
A15: LVM has been in the stock kernel since 2.3.47
|
| 166 |
|
| 167 |
|
| 168 |
Q16: Where can I send a patch for the LVM?
|
| 169 |
|
| 170 |
A16: Please remember to make a unified diff to the original LVM distribution
|
| 171 |
and mail the diff with your comments to
|
| 172 |
<Linux-LVM-Patch@Sistina.com>
|
| 173 |
|
| 174 |
|
| 175 |
Q17: Why am I not able to create my 211th logical volume?
|
| 176 |
vgdisplay tells me about a limit of 256 logical volumes.
|
| 177 |
|
| 178 |
A17: The total amount of 256 logical volumes is shared among all
|
| 179 |
volume groups. You have to delete logical volumes in different
|
| 180 |
volume groups to be able to create the new one.
|
| 181 |
|
| 182 |
|
| 183 |
Q18: Can I have my root filesystem in a logical volume?
|
| 184 |
|
| 185 |
A18: Yes you can. There's basic support since LVM 0.7 to create an initial RAM
|
| 186 |
disk containing the necessary executables, device specials etc.
|
| 187 |
to switch to a logical volume containing e root filesystem.
|
| 188 |
See script lvmcreate_initrd(8).
|
| 189 |
Nevertheless you have to setup the neccesary logical volumes with
|
| 190 |
filesystems, /etc/lilo.conf and /etc/fstab by hand.
|
| 191 |
|
| 192 |
Q19: Why does LVM not support mirroring?
|
| 193 |
|
| 194 |
A19: Mirroring or other levels of RAID on a per Logical Volume
|
| 195 |
base decreases reliability because you have to take care of
|
| 196 |
which Logical Volumes are mirrored and which ones are not.
|
| 197 |
I recommend to use dedicated hardware RAID subsystems or Multiple
|
| 198 |
Devices to have the redundancy below the LVM. In this case you
|
| 199 |
just don't care about Logical Volume data redundancy and you don't
|
| 200 |
run into the dangerous situation that your data is not redundant
|
| 201 |
by accident.
|
| 202 |
If you do have these kind of devices in place you can setup RAID 10/40/50
|
| 203 |
if you want to because the LVM supports RAID0. Combining for eg. several
|
| 204 |
hardware RAID5 subsystems in a volume group to set up LVM-RAID0 gives you
|
| 205 |
reliability, performance and flexibility at the same time.
|
Parent Directory
| 
Revision Log