zfs Snapshot Commands Example

As i have already discussed in my previous post zfs filesystem and MySQL about zfs overview and two most important command zpool and zfs. I am going to continue with usage of zfs snapshots. It includes create a pool, Create file system, Taking a snapshot, Renaming Snapshots, Listing all snapshots, restoring from snapshot and Moving the snapshot to other location.

A snapshot is a read-only copy of a file system or volume. Snapshots can be created almost instantly, and initially consume no additional disk space within the pool. However, as data within the active dataset changes, the snapshot consumes disk space by continuing to reference the old data and so prevents the space from being freed. Snapshots of volumes cannot be accessed directly, but they can be cloned, backed up, rolled back to.

Creating a Pool:

# zpool create zpool1 c2t0d0

List pool:

# zpool list

Create file system under above create pool:

Once you have a storage pool, you can build file systems on it:

# zfs create zpool1/data # zfs create zpool1/logs

Here we have built “/data” file system on pool zpool1

List all zfs file systems:

# zfs list

Taking a Snapshot:

# zfs snapshot < pool name>/<filesystem name>@<snapshot name>

Example:

# zfs snapshot zpool1/data01@Snapshot1

Remove/Destroy a Snapshot:

# zfs destroy < pool name>/<filesystem name>@<snapshot name>

Example:

# zfs destroy zpool1/data01@Snapshot1

Rename Snapshots:

You can rename snapshots but they must be renamed within the pool and dataset from which they were created.

# zfs rename < pool name>/<filesystem name>@<snapshot name> < pool name>/<filesystem name>@<snapshot name>

Example:

# zfs rename zpool1/data01@Snapshot1 zpool1/data01@Snapshot2

Below snapshot rename operation is not supported because the target pool and file system name are different from the pool and file system where the snapshot was created.

# zfs rename zpool1/data01@Snapshot1 zpool3/data01@Snapshot2

Displaying zfs Snapshots:

# zfs list

# zfs list -t snapshot

You can also list snapshots that were created for a particular file system:

# zfs list -r -t snapshot -o <name>,<creation> <pool>/<home>

Restore/Rolling Back zfs snapshots:

# zfs rollback < pool name>/<filesystem name>@<snapshot name>

Example:

# zfs rollback zpool1/data01@Snapshot1

This will restore the entire file system with snapshot.

Restoring individual files:

It is possible to copy individual file from a snapshot by changing into the hidden “.zfs” directory of the pool that has been snapped.

cd /<pool name>/<file system name>

cd .zfs

cp <required file source location> <destination>

Example:

cd /zpool1/data01

cd .zfs

cp <required file source location> <destination>

Moving a  Snapshot to another system:

Wecan move the snapshot to another system and install it there as a usable file system. But at first we need to create a pool to receive the snapshot on the target system.

Step1: Create Pool on another system.

# zpool create -f zpool11 c2t0d0

Step2: Send the snapshot over the network and receive it into the pool using a combination of zfs send/receive command and a netwolrk pipe.

# zfs send zpool1/data01@snapshot1 | ssh <destination host> “usr/sbin/zfs receive zpool11/<myfilesystem>

Here zpool11 is the name of pool on another system which we have created above and myfilesystem is the name of filesystem you wish to put.

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zfs FileSystem and MySQL

ZFS is a new kind of 128-bit file system that provides simple administration, transactional semantics, end-to-end data integrity, and immense scalability. ZFS is not an incremental improvement to existing technology; it is a fundamentally new approach to data management. ZFS was first introduced in Solaris in 2004 and it is a default filesystem in OpenSolaris, but Linux ports are underway, Apple is shipping it in OS X 10.5 Leopard with limited zfs capability ( Apple shutdown this project afterward due to some known reason), and it will be included in FreeBSD 7.

ZFS Features:

• Pooled Storage Model
• Always consistent on disk
• Protection from data corruption
• Live data scrubbing
• Instantaneous snapshots and clones
• Portable snapshot streams
• Highly scalable
• Built in compression
• Simplified administration model

Pooled Storage Model: ZFS presents a pooled storage model that completely eliminates the concept of volumes and the associated problems of partitions, provisioning, wasted bandwidth and stranded storage. Thousands of file systems can draw from a common storage pool, each one consuming only as much space as it actually needs. The combined I/O bandwidth of all devices in the pool is available to all file systems at all times.

Always consistent on disk: All operations are copy-on-write transactions, so the on-disk state is always valid. Every block is checksummed to prevent silent data corruption, and the data is self-healing in replicated (mirrored or RAID) configurations. If one copy is damaged, ZFS detects it and uses another copy to repair it.

Protection from data corruption: ZFS introduces a new data replication model called RAID-Z. It is similar to RAID-5 but uses variable stripe width to eliminate the RAID-5 write hole (stripe corruption due to loss of power between data and parity updates). All RAID-Z writes are full-stripe writes. There's no read-modify-write tax, no write hole, and — the best part — no need for NVRAM in hardware. ZFS loves cheap disks.

Live data scrubbing: But cheap disks can fail, so ZFS provides disk scrubbing. Similar to ECC memory scrubbing, all data is read to detect latent errors while they're still correctable. A scrub traverses the entire storage pool to read every data block, validates it against its 256-bit checksum, and repairs it if necessary. All this happens while the storage pool is live and in use.
ZFS has a pipelined I/O engine, similar in concept to CPU pipelines. The pipeline operates on I/O dependency graphs and provides scoreboarding, priority, deadline scheduling, out-of-order issue and I/O aggregation. I/O loads that bring other file systems to their knees are handled with ease by the ZFS I/O pipeline.

Instantaneous snapshots and clones (Most important and useful for huge backups in seconds): ZFS provides 2 64 constant-time snapshots and clones. A snapshot is a read-only point-in-time copy of a file system, while a clone is a writable copy of a snapshot. Clones provide an extremely space-efficient way to store many copies of mostly-shared data such as workspaces, software installations, and diskless clients.

Portable snapshot streams (Important & useful feature): You snapshot a ZFS file system, but you can also create incremental snapshots. Incremental snapshots are so efficient that they can be used for remote replication, such as transmitting an incremental update every 10 seconds.

Highly scalable (Important  useful feature): There are no arbitrary limits in ZFS. You can have as many files as you want: full 64-bit file offsets, unlimited links, directory entries, and so on.

Built in compression: ZFS provides built-in compression. In addition to reducing space usage by 2-3x, compression also reduces the amount of I/O by 2-3x. For this reason, enabling compression actually makes some workloads go faster.
In addition to file systems, ZFS storage pools can provide volumes for applications that need raw-device semantics. ZFS volumes can be used as swap devices, for example. And if you enable compression on a swap volume, you now have compressed virtual memory.

Simplified administration model: ZFS administration is both simple and powerful. zpool and zfs are the only two command you need to know. Please see the zpool(1M) and zfs(1M) man pages for more information.

The storage pool is a key abstraction: a pool can consist of many physical devices, and can hold many filesystems. Whenever you add storage to the pool, it becomes available to any filesystem that may need it. To take a newly-attached disk and use the whole disk for ZFS storage, you would use the command.

# zpool create zpool1 c2t0d0

Here, zpool1 represents the name of a pool, and c2t0d0 is a disk device.

If you have a disk had already been formatted – say, with a UFS filesystem on one partition – you can create a storage pool from another free partition:

# zpool create zpool1 c2t0d0s2 

You can even use a plain file for storage:

# zpool create zpool1 ~/storage/myzfile

Once you have a storage pool, you can build filesystems on it:

# zfs create zpool1/data # zfs create zpool1/logs 

Later on, if you run out of space, just add another device to the pool, and the filesystem will grow.

# zpool add zp1 c3t0d0

ZFS and Tablespaces:

innodb_data_file_path = /dbzpool/data/ibdatafile:20G:autoextend

Here is the only innodb_data_file_path that any ZFS system might ever need. You can split this over as many drives as you want, and ZFS will balance the load intelligently. You can stripe it, mirror it, add space when you need room to grow, bring spare disks online, and take faulted disks offline, without ever restarting the database.

Please refer Best practice guide for zfs and zfs evil tuning guide

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