ASM Dynamic Volume Manager and ASM Clustered File System

Two of the top features in 11gR2 are the ASM Dynamic Volume Manager (ADVM) and ASM Clustered File System (ACFS). What is the big deal about these two?

ADVM allows you to create a volume from an ASM diskgroup. Here is an example where we created a volume called asm_vol1 of 100 MB on a diskgroup called DATA:

ASMCMD [+] > volcreate -G DATA -s 100M asm_vol1

Internally it issues the command

alter diskgroup DATA add volume 'asm_vol1' size 100M;

Now you enable the volume you just created:

ASMCMD [+] > volenable -G DATA asm_vol1

Internally it issues:

alter diskgroup DATA enable volume 'asm_vol1';

You can perform other commands like resize, delete, disable; but more on that later on a full length article.

Now that the volume is created, what can you do with it. Well, like all volumes, you can create a filesystem on it. Here is an example of creating a FS called acfs1:

[root@oradba2 ~]# mkdir /acfs1
[root@oradba2 ~]# /sbin/mkfs -t acfs /dev/asm/asm_vol1-207
mkfs.acfs: version                   = 11.2.0.1.0.0
mkfs.acfs: on-disk version           = 39.0
mkfs.acfs: volume                    = /dev/asm/asm_vol1-207
mkfs.acfs: volume size               = 268435456

Register MountPoint Command:

[root@oradba2 ~]# /sbin/acfsutil registry -a -f /dev/asm/asm_vol1-207 /acfs1
acfsutil registry: mount point /acfs1 successfully added to Oracle Registry

If you get an error, use the force option:

[root@oradba2 /]# /sbin/mkfs.acfs -f /dev/asm/asm_vol1-207
mkfs.acfs: version                   = 11.2.0.1.0.0
mkfs.acfs: on-disk version           = 39.0
mkfs.acfs: volume                    = /dev/asm/asm_vol1-207
mkfs.acfs: volume size               = 268435456
mkfs.acfs: Format complete.

Now you mount the the filesystem:

[root@oradba2 /]# /bin/mount -t acfs /dev/asm/asm_vol1-207 /acfs1

Now if you will check the filesystem, you will notice a new one - /acfs1

[root@oradba2 /]# df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                     149313708  22429752 119176924  16% /
/dev/sda1               101086     11765     84102  13% /boot
tmpfs                   907628    591640    315988  66% /dev/shm
/dev/asm/asm_vol1-207
                        262144     37632    224512  15% /acfs1

This new filesystem is actually carved out of the ASM diskspace. This can be used as a regular filesystem:

[root@oradba2 /]# cd /acfs1
[root@oradba2 acfs1]# ls
lost+found
[root@oradba2 acfs1]# touch 1

So, what't the big deal about it? Plenty.

First, this is part of the ASM management; so all the bells and whistles of ASM - such as asynch i/o, etc. - applies to this filesystem.

Second, this is now a "cluster" filesystem; it is visible across a cluster. So, now you have a fully functional generic filesystem visible across the cluster.

Third, this is now protected by the Grid infrastructure, if you have installed it. Remember from my earlier posts that in 11gR2 you can now have a restartable grid infrastructure even on a single instance.

More on ASM Dynamic Volume Manager later in a full length article. But I hope this makes you really interested.