Exercise #4: Snapshots

In this lab we will use the snapshot feature to create online copies of files.

Objectives:

Create a file system snapshot
Restore a user deleted file from a snapshot image
Manage multiple snapshot images

Requirements:

Complete Exercise 1: Installing the cluster
A File System - Use Exercise 2 to create a file system if you do not already have one.

Step 1: Use a snapshot to backup a file

A snapshot is a point in time view of a file system. To see how snapshots operate you will create a file, take a snapshot, delete the file then restore the snapshot from the file.

Create a file for testing in the /gpfs/fileset1 directory.
```
echo "hello world:snap1" > /gpfs/fileset1/snapfile1
```

Create a snapshot image using the mmcrsnapshot command

								# mmcrsnapshot fs1 snap1

Writing dirty data to disk
Quiescing all file system operations
Writing dirty data to disk again
Creating snapshot.
Resuming operations.

Modify the file for testing in the /gpfs/fileset1 directory.
```
echo "hello world:snap2" >> /gpfs/fileset1/snapfile1
```
Create a seconds snapshot image using the mmcrsnapshot command
```
mmcrsnapshot fs1 snap2
```

View the list of snapshots created using the mmlssnapshot command

								Example:
# mmlssnapshot fs1
gpfs1:~ # mmlssnapshot fs1
Snapshots in file system fs1:
Directory    SnapId    Status       Created
snap1        2         Valid        Wed Sep 26 11:03:52 2007
snap2        3         Valid        Wed Sep 26 11:04:52 2007

Delete the file /gpfs/fileset1/snapfile1 Now that the file is deleted let's see what is in the snapshots:
Take a look at the snapshot images. To view the image change directories to the .snapshot directory
```
cd /gpfs/.snapshots
```
What directories do you see? _____________________
Compare the snapfile1 stored in each snapshot
```
cat snap1/fileset1/snapfile1
```
```
cat snap2/fileset1/snapfile1
```
Are the file contents the same? _______________
To restore the file from the snapshot copy the file back into the original location
```
cp /gpfs/.snapshots/snap1/fileset1/snapfile1 /gpfs/fileset1/snapfile1
```
When you are done with a snapshot you can delete the snapshot. Delete both of these snapshots using the mmdelsnapshot command
```
mmdelsnapshot fs1 snap1
mmdelsnapshot fs1 snap2
```
Verify the snapshots were deleted using the mmlssnapshot command
```
mmlssnapshot fs1
```