一、lvm條帶化的概念
一般以LVM管理的存儲，一個vg中可能會有很多pv，同樣的，一個lv可能跨越多塊pv，爲了使硬盤存儲速度加快，就會用到條帶化的技術，即把連續的數據分成大小相同的數據塊，然後依次存儲在各個pv上。
類似於RAID0，使存儲速度加快。但並不會使數據像RAID0一樣危險容易丟失，因爲在正式使用中，不會像此時做測試一樣沒有任何保障地將多塊硬盤做成一個vg，而是普遍連接的後臺存儲，在劃分LUN之前，
已經在物理硬盤上做好RAID5或RAID1，在RAID5或RAID1的基礎上再劃分出多塊LUN,即系統上的pv，即使pv所在硬盤損壞，但有底層的硬RAID冗餘，並不會丟失數據。
條帶單元大小：即條帶化的LV中，每一個條帶單元的大小，對應於I/O中數據塊的大小。對於Oracle來講，db_block_size即設定的數據塊大小。而db_file_multiblock_read_count就一次讀取時最多並行的數據塊的個數，
db_block_size和db_file_multiblock_read_count相乘即一次總的I/O大小。這個大小不能超過操作系統的最大I/O (max_io_size)值。在ORACLE應用中，lv條帶的大小一般設置爲兩倍或兩倍以上的Oracle塊大小，
因爲假如設置成與Oracle數據塊相同大小，無法保證Oracle數據塊的邊界正好與條帶單元的邊界對應，如果不對應的話，就會出現大量的一個I/O由兩個條帶單元，來處理的情況。
條帶大小的原則：對於高併發並且IO請求小的情況下，一塊物理硬盤處理多個I/O請求，低併發但I/O請求較大時，可能需要多塊硬盤處理一個I/O請求。原則上的要求是一次I/O請求能被一次性處理完成。
大概的條帶化的概念就是這樣。
二、條帶化lv的創建
先看本機中的VG情況，只有一個vg00，物理硬盤個數是從/dev/sdd到/dev/sdi一共6塊。
[[email protected] ~]# vgscan
Reading all physical volumes. This may take a while...
Found volume group "vg00" using metadata type lvm2
將每塊硬盤做爲一個PV，先全部執行完成。爲了一會做lvextend的測試，先用前三塊硬盤創建vg01
[[email protected] ~]# pvcreate /dev/sdd /dev/sde /dev/sdf /dev/sdg /dev/sdh /dev/sdi
Physical volume "/dev/sdd" successfully created
Physical volume "/dev/sde" successfully created
Physical volume "/dev/sdf" successfully created
Physical volume "/dev/sdg" successfully created
Physical volume "/dev/sdh" successfully created
Physical volume "/dev/sdi" successfully created
[[email protected] ~]# vgcreate /dev/vg01 /dev/sdd /dev/sde /dev/sdf
Volume group "vg01" successfully created
[[email protected] ~]# vgdisplay vg01
--- Volume group ---
VG Name vg01
System ID
Format lvm2
Metadata Areas 3
Metadata Sequence No 1
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 0
Open LV 0
Max PV 0
Cur PV 3
Act PV 3
VG Size 5.99 GB
PE Size 4.00 MB
Total PE 1533
Alloc PE / Size 0 / 0
Free PE / Size 1533 / 5.99 GB
VG UUID W6EwVP-YIva-iCqr-KuZf-B3jt-4cA3-4XcSv4
再創建條帶化的lv，下面用到的lvextend的參數如下：
-i:此處寫lv用到的pv的數量，不能超過所在vg的pv數量，一般設置與vg的pv個數相同
-I:條帶單元大小，單位Kb
-L:lv的大小，默認爲Mb,可帶單位G,M,K
-l:小寫L，分配給lv的LE個數，對應於VG中的PE，在上條vgdisplay的輸出中可看到VG中一共有1533個PE。
-n:自定義lv的名字，默認從lvol0開始往下排。
爲了下面測試條帶化下的lvextend，所以將此vg的所有空間都給這個lv，即1533個LE，一共5.99G的可用空間。
[[email protected] ~]# lvcreate -i 3 -I 64 -l 1533 -n stripe_lv vg01
Logical volume "stripe_lv" created
[[email protected] ~]# lvdisplay /dev/vg01/stripe_lv
--- Logical volume ---
LV Name /dev/vg01/stripe_lv
VG Name vg01
LV UUID TyF4aW-gegH-Vmxi-hWUl-a7t7-Vw5V-B64Eik
LV Write Access read/write
LV Status available
# open 0
LV Size 5.99 GB
Current LE 1533
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 768
Block device 253:4
執行格式化和掛載
[[email protected] ~]# mkfs.ext3 /dev/vg01/stripe_lv
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
784896 inodes, 1569792 blocks
78489 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=1610612736
48 block groups
32768 blocks per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 24 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
[[email protected] ~]# mkdir /stripe
[[email protected] ~]# mount /dev/vg01/stripe_lv /stripe/
[[email protected] ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg00-lv_root 6.0G 398M 5.3G 7% /
/dev/mapper/vg00-lv_usr 6.8G 1.7G 4.8G 26% /usr
/dev/mapper/vg00-lv_data 93M 5.6M 83M 7% /data
/dev/sdc1 988M 24M 914M 3% /boot
/dev/mapper/vg01-stripe_lv 5.9G 141M 5.5G 3% /stripe
三、條帶化lv的擴展
然後測試給此條帶化的lv擴容，先vgextend,再lvextend.
條帶化的lv擴展需要新增pv的時候，有個重要條件，增加的pv數量必須與lv現有的pv數量相同或成倍數關係。想想RAID0的原理就知道了，抽象地說，數據分成大小相同的數據塊，然後依次存儲在每塊硬盤，如果要擴大，必然要每塊硬盤都相應擴大。此處先只增加一塊硬盤看是否可以。
[[email protected] ~]# vgextend /dev/vg01 /dev/sdg
Volume group "vg01" successfully extended
增加硬盤後，可以看到vg size變大爲7.98G，並且PE數量變爲2044，pv數量變爲4個。
[[email protected] ~]# vgdisplay /dev/vg01
--- Volume group ---
VG Name vg01
System ID
Format lvm2
Metadata Areas 4
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 4
Act PV 4
VG Size 7.98 GB
PE Size 4.00 MB
Total PE 2044
Alloc PE / Size 1533 / 5.99 GB
Free PE / Size 511 / 2.00 GB
VG UUID W6EwVP-YIva-iCqr-KuZf-B3jt-4cA3-4XcSv4
因爲有2G的可用空間，此處試着增加100M，但是結果是失敗的，提示不夠用。
[[email protected] ~]# lvextend -L+100 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Rounding size (1558 extents) down to stripe boundary size for segment (1557 extents)
Extending logical volume stripe_lv to 6.08 GB
Insufficient suitable allocatable extents for logical volume stripe_lv: 24 more required
然後再以LE的方式增加，一共有511個可用的PE，即最大應該可增加511個LE，此處只增加10個仍然失敗，提示需要額外的9個。
[[email protected] ~]# lvextend -l+10 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Rounding size (1543 extents) down to stripe boundary size for segment (1542 extents)
Extending logical volume stripe_lv to 6.02 GB
Insufficient suitable allocatable extents for logical volume stripe_lv: 9 more required
看起來增加1個應該可以，每次執行也都提示成功。但是每次都提示增加到1534個LE。
[[email protected] ~]# lvextend -l+1 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Rounding size (1534 extents) down to stripe boundary size for segment (1533 extents)
Extending logical volume stripe_lv to 5.99 GB
Logical volume stripe_lv successfully resized
[[email protected] ~]# lvextend -l+1 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Rounding size (1534 extents) down to stripe boundary size for segment (1533 extents)
Extending logical volume stripe_lv to 5.99 GB
Logical volume stripe_lv successfully resized
然後以lvdisplay查看，LE的數量仍爲1533，並未增加。至於爲何會顯示增加1個成功，就不曉得了~~~但從結果知道，其實並沒有增加
[[email protected] ~]# lvdisplay /dev/vg01/stripe_lv
--- Logical volume ---
LV Name /dev/vg01/stripe_lv
VG Name vg01
LV UUID TyF4aW-gegH-Vmxi-hWUl-a7t7-Vw5V-B64Eik
LV Write Access read/write
LV Status available
# open 1
LV Size 5.99 GB
Current LE 1533
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 768
Block device 253:4
再把剩餘的另外2個pv加上，就一共增加了3個pv，正好與vg01的原pv數量相同，成倍數關係。此時vg01的pv個數變成了6個，是原來的2倍。
[[email protected] ~]# vgextend /dev/vg01 /dev/sdh /dev/sdi
Volume group "vg01" successfully extended
[[email protected] ~]# vgdisplay /dev/vg01
--- Volume group ---
VG Name vg01
System ID
Format lvm2
Metadata Areas 6
Metadata Sequence No 7
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 6
Act PV 6
VG Size 11.98 GB
PE Size 4.00 MB
Total PE 3066
Alloc PE / Size 1788 / 6.98 GB
Free PE / Size 1278 / 4.99 GB
VG UUID W6EwVP-YIva-iCqr-KuZf-B3jt-4cA3-4XcSv4
再用lvextend擴展空間，分別從LE和SIZE的角度擴展，均提示成功。
[[email protected] ~]# lvextend -L+1024 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Rounding size (1789 extents) down to stripe boundary size for segment (1788 extents)
Extending logical volume stripe_lv to 6.98 GB
Logical volume stripe_lv successfully resized
[[email protected] ~]# resize2fs /dev/vg01/stripe_lv
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/vg01/stripe_lv is mounted on /stripe; on-line resizing required
Performing an on-line resize of /dev/vg01/stripe_lv to 1830912 (4k) blocks.
The filesystem on /dev/vg01/stripe_lv is now 1830912 blocks long.
[[email protected] ~]# lvdisplay /dev/vg01/stripe_lv
--- Logical volume ---
LV Name /dev/vg01/stripe_lv
VG Name vg01
LV UUID TyF4aW-gegH-Vmxi-hWUl-a7t7-Vw5V-B64Eik
LV Write Access read/write
LV Status available
# open 1
LV Size 6.98 GB
Current LE 1788
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 768
Block device 253:4
[[email protected] ~]# lvextend -l+1278 /dev/vg01/stripe_lv
Using stripesize of last segment 64.00 KB
Extending logical volume stripe_lv to 11.98 GB
Logical volume stripe_lv successfully resized
[[email protected] ~]# resize2fs /dev/vg01/stripe_lv
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/vg01/stripe_lv is mounted on /stripe; on-line resizing required
Performing an on-line resize of /dev/vg01/stripe_lv to 3139584 (4k) blocks.
The filesystem on /dev/vg01/stripe_lv is now 3139584 blocks long.
[[email protected] ~]# lvdisplay /dev/vg01/stripe_lv
--- Logical volume ---
LV Name /dev/vg01/stripe_lv
VG Name vg01
LV UUID TyF4aW-gegH-Vmxi-hWUl-a7t7-Vw5V-B64Eik
LV Write Access read/write
LV Status available
# open 1
LV Size 11.98 GB
Current LE 3066
Segments 2
Allocation inherit
Read ahead sectors auto
- currently set to 768
Block device 253:4
查看大小
[[email protected] ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg00-lv_root 6.0G 398M 5.3G 7% /
/dev/mapper/vg00-lv_usr 6.8G 1.7G 4.8G 26% /usr
/dev/mapper/vg00-lv_data 93M 5.6M 83M 7% /data
/dev/sdc1 988M 24M 914M 3% /boot
/dev/mapper/vg01-stripe_lv 12.0G 141M 11.6G 97% /stripe
4.4.12. Growing Logical Volumes
To increase the size of a logical volume, use the lvextend command.
When you extend the logical volume, you can indicate how much you want to extend the volume, or how large you want it to be after you extend it.
The following command extends the logical volume /dev/myvg/homevol to 12 gigabytes.
# lvextend -L12G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 12 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
The following command adds another gigabyte to the logical volume /dev/myvg/homevol.
# lvextend -L+1G /dev/myvg/homevol
lvextend -- extending logical volume "/dev/myvg/homevol" to 13 GB
lvextend -- doing automatic backup of volume group "myvg"
lvextend -- logical volume "/dev/myvg/homevol" successfully extended
As with the lvcreate command, you can use the -l argument of the lvextend command to specify the number of extents by which to increase the size of the logical volume. You can also use this argument to specify a percentage of the volume group, or a percentage of the remaining free space in the volume group. The following command extends the logical volume called testlv to fill all of the unallocated space in the volume group myvg.
[root@tng3-1 ~]# lvextend -l +100%FREE /dev/myvg/testlv
Extending logical volume testlv to 68.59 GB
Logical volume testlv successfully resized
After you have extended the logical volume it is necessary to increase the file system size to match.
By default, most file system resizing tools will increase the size of the file system to be the size of the underlying logical volume so you do not need to worry about specifying the same size for each of the two commands.
4.4.12.1. Extending a Striped Volume
In order to increase the size of a striped logical volume, there must be enough free space on the underlying physical volumes that make up the volume group to support the stripe. For example, if you have a two-way stripe that that uses up an entire volume group, adding a single physical volume to the volume group will not enable you to extend the stripe. Instead, you must add at least two physical volumes to the volume group.
For example, consider a volume group vg that consists of two underlying physical volumes, as displayed with the following vgs command.
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 2 0 0 wz--n- 271.31G 271.31G
You can create a stripe using the entire amount of space in the volume group.
# lvcreate -n stripe1 -L 271.31G -i 2 vg
Using default stripesize 64.00 KB
Rounding up size to full physical extent 271.31 GB
Logical volume "stripe1" created
# lvs -a -o +devices
LV VG Attr LSize Origin Snap% Move Log Copy% Devices
stripe1 vg -wi-a- 271.31G /dev/sda1(0),/dev/sdb1(0)
Note that the volume group now has no more free space.
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 2 1 0 wz--n- 271.31G 0
The following command adds another physical volume to the volume group, which then has 135G of additional space.
# vgextend vg /dev/sdc1
Volume group "vg" successfully extended
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 3 1 0 wz--n- 406.97G 135.66G
At this point you cannot extend the striped logical volume to the full size of the volume group, because two underlying devices are needed in order to stripe the data.
# lvextend vg/stripe1 -L 406G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 406.00 GB
Insufficient suitable allocatable extents for logical volume stripe1: 34480
more required
To extend the striped logical volume, add another physical volume and then extend the logical volume. In this example, having added two physical volumes to the volume group we can extend the logical volume to the full size of the volume group.
# vgextend vg /dev/sdd1
Volume group "vg" successfully extended
# vgs
VG #PV #LV #SN Attr VSize VFree
vg 4 1 0 wz--n- 542.62G 271.31G
# lvextend vg/stripe1 -L 542G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 542.00 GB
Logical volume stripe1 successfully resized
If you do not have enough underlying physical devices to extend the striped logical volume, it is possible to extend the volume anyway if it does not matter that the extension is not striped, which may result in uneven performance. When adding space to the logical volume, the default operation is to use the same striping parameters of the last segment of the existing logical volume, but you can override those parameters. The following example extends the existing striped logical volume to use the remaining free space after the initial lvextend command fails.
# lvextend vg/stripe1 -L 406G
Using stripesize of last segment 64.00 KB
Extending logical volume stripe1 to 406.00 GB
Insufficient suitable allocatable extents for logical volume stripe1: 34480
more required
# lvextend -i1 -l+100%FREE vg/stripe1