ORACLE AU TOMATIC STORAGE
MANAGEMENT CLUS TER FILE SYS TEM
COMPONENTS
To help the team understand how Oracle
Automatic Storage Management Cluster
File System works, John draws everyone’s
attention to Figure 1, which shows various
components of Oracle Automatic Storage
Management Cluster File System. One or
more disks make up an Oracle Automatic
Storage Management disk group—shown
in the figure as ACFSDG1—on which one or
more Oracle Automatic Storage Management
volumes can be created. John points to the
two Oracle Automatic Storage Management
volumes in the figure—acfsvol1 and
acfsvol2—and then to the two file systems—
/acfsdir1 and /acfsdir2—on those volumes.
As long as free space exists inside the disk
group, the volumes can be expanded and the
file system will expand as well.
When users access the file system, a
component called Oracle Automatic Storage
Management Dynamic Volume Manager
translates the I/O calls and fetches the
data from the appropriate location on the
disk. The presence of this Oracle Automatic
Storage Management Dynamic Volume
Manager component, John points out, is
what makes the volumes dynamic (and not
bound to a physical device). Because of this
component, new disks can be added and
old ones removed, but nothing happens to
the data on the volumes and file systems—
making applications resilient.
John also mentions that when the system
reboots, the file system does not by default
remount automatically. The Oracle grid
infrastructure can mount the file system
after a reboot, but the volume must be
registered in its registry. John shows how
to register the Oracle Automatic Storage
Management volume in the registry by using
a utility called acfsutil, installed in the /sbin
directory as part of the Oracle grid infrastructure installation:
acfsutil registry -a /dev/asm
/acfsvol1a-153 /acfsdir1
acfsutil registry: mount point /acfsdir1
successfully added to Oracle Registry
The grid infrastructure registry, John
explains, acts as a clusterwide file system
reference file, much like the /etc/fstab file
on a Linux system. After the file system is
mounted in the registry, it is automatically
brought up after a node reboots or the
grid restarts.
So . . . you want a
regular file system
that’s visible across
all the nodes of an
Oracle RAC cluster.
ORACLE AUTOMATIC STORAGE
MANAGEMENT CLUSTER FILE S YSTEM
SNAPSHOTS
Ben then asks, “What about my requirement
to automatically save files before modification?” John demonstrates how easy it
would be to perform that task. He describes
another feature of Oracle Automatic Storage
Management Cluster File System—called
snapshots—that literally takes snapshots
of the changed blocks of a file at a different
location. To conserve space, snapshots work
at the block level instead of the file level.
When a file is modified, only the changed
blocks are copied over to the new location.
To demonstrate, John shows a listing of the
files in the directory:
ls -l
total 72
-rw-r--r-- 1 oracle dba 218 May 25
17: 57 file1.gif
-rw-r--r-- 1 oracle dba 436 May 25
17: 57 file2.gif
drwx------ 2 root root 65536 May 25
17: 11 lost+found
He then creates a snapshot called
backup1:
Issue
A regular file system is not visible across multiple servers.
Table 1: Issues and their solutions
Files cannot be tracked during modification, and backup does
not guarantee consistency.
Space and growth requirements are not known at deployment.
/sbin/acfsutil snap create backup1
/acfsdir1
acfsutil snap create: Snapshot operation
is complete.
This operation creates a directory called
backup1 inside a directory called snaps
under a hidden directory called .ACFS (note
the leading period). This directory contains
modified file blocks. To trigger an automatic
backup, John deletes a file:
rm file2.gif
He then demonstrates how the file is still
available in the .ACFS location:
ls -l .ACFS/snaps/*/ file2.gif
-rw-r--r-- 1 oracle dba 218 May 25 17: 57
.ACFS/snaps/backup1/ file1.gif
When the snapshots are first created
on the file system, he stresses, nothing is
actually stored, so there is no space consumption. When the file is deleted, the previous images of the file blocks are copied
to the snapshot. So if Ben ever wants to go
back to a previous version of the file, he can
access the snapshot. Similarly, he can also
copy the snapshots to tape to create a consistent backup set of the files. He couldn’t
be happier.
ORACLE AUTOMATIC S TORAGE
MANAGEMENT CLUS TER FILE SYS TEM
ADMINISTRATION
“It sounds too good to be true,” opines a
skeptical Craig. He isn’t sure how flexible
the system is and wants to know how difficult it is to manage. John assures him
that administration is a breeze with either
regular SQL, the ASMCMD command-line
tool, or Oracle Enterprise Manager. With
some example operations, he demonstrates
the fine level of detail enabled by Oracle
Solution
Oracle Automatic Storage Management Cluster File System, a
regular (cooked) file system that is clustered
Snapshots, which store previous images of changed blocks—not
complete files—in case of modifications (to save space)
Online dynamic resizing of volumes
