Dell Enterprise Solution Resources Owner's manual

Dell
Brand
Dell
Model
Enterprise Solution Resources
Type
Owner's manual

This manual is also suitable for

A Dell Best Practices Guide
Dell PS Series: Space Borrowing for Snapshots and
Replicas
Dell PS Series firmware v8.0
Dell Storage Engineering
November 2019
2 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Revisions
Date
Description
September 2012
Initial release
May 2015
Updates for Dell PS Series firmware v8.0, including Space Borrowing for Replication
November 2019
vVols branding update
THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS
PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND.
© 2015–2019 Dell Inc. All rights reserved. Dell, the DELL logo, and the DELL badge are trademarks of Dell Inc. Other trademarks and trade names may be used in this
document to refer to either the entities claiming the marks and names or their products. Dell disclaims any proprietary interest in the marks and names of others.
3 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Table of contents
Revisions ............................................................................................................................................................................................... 2
Audience ............................................................................................................................................................................................... 4
Objective .............................................................................................................................................................................................. 4
Introduction.......................................................................................................................................................................................... 4
1 Space borrowing ........................................................................................................................................................................... 5
1.1 Snapshots ........................................................................................................................................................................... 6
1.1.1 Snapshot reserve ................................................................................................................................................................ 6
1.2 Asynchronous replication ................................................................................................................................................... 8
1.2.1 Replication Space ............................................................................................................................................................... 9
2 Best practices for space borrowing ............................................................................................................................................. 10
2.1 Planning space requirements ........................................................................................................................................... 10
2.2 Space borrowing prioritization ......................................................................................................................................... 10
2.3 Space borrowing behavior with changes to storage pools............................................................................................... 10
2.4 Space borrowing for replication ....................................................................................................................................... 10
3 Space borrowing with thin provisioned volumes and SCSI UNMAP ........................................................................................... 12
4 Displaying borrowed space information ..................................................................................................................................... 13
4.1.1 Local Space tab ................................................................................................................................................................. 15
4.1.2 Remote Delegated Space tab ........................................................................................................................................... 18
5 Space borrowing examples ......................................................................................................................................................... 20
5.1.1 Space borrowing with snapshots...................................................................................................................................... 20
5.1.2 Space borrowing with snapshots and replication schedules ............................................................................................ 21
5.1.3 Space borrowing with low delegated space on the secondary group (replication) ......................................................... 23
5.1.4 Space borrowing with low total replica reserve (replication) .......................................................................................... 26
A Additional resources ................................................................................................................................................................... 30
A.1 Related documentation .................................................................................................................................................... 30
4 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Audience
The information in this guide is intended for technology professionals interested in using Dell PS Series storage to
protect and recover data using PS Series snapshots and replicas.
Objective
This guide details the space borrowing features in Dell PS Series firmware v8.0 and later for snapshots and replicas.
Introduction
Storage plays a critical role in business operations. With the ever-growing presence of new applications and data,
storage demands continue to grow. Dell PS Series provides support for block storage with PS Series firmware, and
Network Attached Storage (NAS) with FS Series firmware, delivering high performance, high availability, scalability, and
on-demand provisioning in a unified storage environment.
5 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1 Space borrowing
In a Dell PS Series group, snapshots and replicas are space-efficient, point-in-time copies of a volume that can be used
to protect data and are often used to recover data lost by human error and data corruption.
Snapshots and replicas require available disk space to operate successfully. This disk space is referred to as snapshot
reserve and replica reserve. To determine the optimal amount of reserve space for snapshots and replicas, it is a best
practice to use the default space values, monitor activity over time, analyze the space usage, and make adjustments as
necessary. These precautions will help you keep the desired number of snapshots and replicas while using space
efficiently.
Space usage is not always predictable, however, and sometimes it is difficult to determine the optimal values to use for
reserves. For example, if reserves are set too high, then space is wasted. If reserves are set too low, then it is difficult to
maintain the desired number of snapshots and replicas to keep. If, for example, free reserve space is low in a pool for
snapshots, or within delegated space for replicas, then creating another snapshot or replica can potentially force older
snapshots and replicas to be prematurely deleted.
Dell PS Series firmware version 8.0 provides the ability for snapshots, local and remote replicas, and deleted volumes in
the Group Volume Recovery Bin to temporarily borrow space beyond the configured reserves. This feature, called
space borrowing, simplifies configuring reserve space, improves space utilization, and enhances management of
snapshots and replica reserves.
Note: Previous versions of Dell PS Series firmware (6.x and 7.x) provided space borrowing for snapshots and local
replication operations only.
Borrowed space is a subset of the storage pool’s total space and can allow older snapshots and replicas to remain if
space is available to borrow. Borrowed space is automatically reclaimed when necessary. Space is potentially available
for borrowing from the following areas:
• Unused snapshot reserve
• Unused local replication reserve on the primary and secondary groups
• Unused delegated space
• Free space in the storage pool where the snapshot or replica resides; space cannot be borrowed from another
pool.
Space cannot be borrowed from:
• Unused volume reserve: Unused Space that has been reserved for volumes.
• NAS storage container: NAS containers are used by Dell Storage FS Series nodes to create NAS shares. Since these
volumes do not contain PS Series snapshots or replicas, they are not available for space borrowing.
• VMware® vSphere® Virtual volumes™ (vVols) storage container: vVol storage containers are used with VMware
environments and cannot be used to hold standard PS Series volumes, snapshots, replicas, or NAS containers.
Storage containers are not supported outside of the VMware Virtual Volumes context.
For examples on using Space Borrowing with Snapshots and Replicas, please refer to: Space Borrowing Examples.
6 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1.1 Snapshots
In a PS Series group, Snapshots are space-efficient, point-in-time copies of a volume that can be used to protect data
and are often used to recover data lost by human error and data corruption. Multiple snapshots of a volume can be
retained for data protection and are accessible to other hosts.
When a Snapshot of a volume is created, it does not initially consume any space (as the snapshot shares all data with
the volume), but instead is a set of pointers to the data in the base volume. As data is modified on the base volume,
disk space is allocated from the snapshot reserve to store the modified data. Meanwhile, the snapshot still points to
the original data pages so that the volume looks exactly like it did at the point in time when the snapshot was taken.
1.1.1 Snapshot reserve
In order to create snapshots of a volume, the administrator must allocate snapshot reserve to hold the snapshot data.
Snapshot reserve space is consumed from the local group and pool where the volume resides and is a percentage of a
volume to be used to store its snapshots.
Note: Because snapshot reserve is a percentage of the volume reserve, the amount of snapshot reserve space
fluctuates in direct proportion to a thin-provisioned volume reserve when data is dynamically written and deleted (for
example, when invoking SCSI UNMAP from Microsoft
®
Windows
®
, VMware
®
ESXi™ or Red Hat
®
Linux — see section 3).
7 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1.1.1.1 Snapshot reserve settings
Depending on the number of snapshots and the amount of changes made to the base volume, snapshot reserve can
become entirely consumed. If this happens, the default action is to delete the oldest snapshot, providing the necessary
free space to create a new snapshot. However, there are various other configurable defaults for snapshot space.
Default Snapshot reserve settings can be managed at the PS Series group level, and at the individual volume level.
Note: Modifying default Snapshot space settings at the group level affects subsequently created volumes, not existing
volumes.
To modify the default Snapshot policy for the entire PS Series group:
1. In Group Manager, select the group in the left pane.
2. Click Group Configuration.
3. Click the Defaults tab.
Snapshot space reserve settings use group default values, unless you explicitly change them for an individual volume.
Table 1 Snapshot reserve settings
Item
Description
Snapshot space reserve
Amount of snapshot storage space, based on a percentage of the volume,
reserved in the local storage pool. If the size of a volume changes, the amount
of snapshot reserve also changes.
Warn when in-use space
reaches this percentage of
snapshot reserve
Percentage of the snapshot reserve, when reached by in-use snapshot reserve,
results in an event message. The default is 90 percent of the snapshot reserve.
Snapshot space recovery
policy
• Set the volume (and snapshots) offline
• Delete the oldest snapshots to free space for new snapshots
• Borrow snapshot space as needed
To modify the Snapshot policy for an individual volume:
4. In Group Manager, click the group in the left pane.
8 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
5. Expand Volumes, right-click the volume and select Modify snapshot policy.
6. Select a snapshot space recovery option and click OK.
7. To enable space borrowing for snapshots, check Borrow snapshot space as needed.
For additional information on snapshots, refer to the following documents.
• Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
• Dell PS Series Snapshots and Clones: Best Practices and Sizing Guidelines
1.2 Asynchronous replication
Replicas are also space-efficient, point-in-time copies of a volume that can be used to protect and recover data.
However, while snapshots of a volume reside in the same pool and PS Series group as the base volume, replicas of a
volume reside in a pool of a secondary PS Series group. Volume replication between two PS Series groups provides
protection against data loss. If a volume is destroyed in a primary PS Series group, you can fail over and recover the
data from a replica in a Secondary PS Series group. This is commonly used to provide business continuity in disaster
recovery situations such as regional disasters and testing scenarios.
9 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1.2.1 Replication Space
Volume replication between partners requires space on both the primary group (the volume location) and the
secondary group (the replica location). These space requirements are classified as follows:
Delegated space on the secondary group, is the amount of space dedicated to storing replicas from the primary group.
All replica reserves are confined to exist within this configured limit.
Local replication reserve on the primary group, is the amount of space reserved in the pool for replication operations.
Current replica volume reserve (in MB/GB/TB) on the secondary group, is the reserved space for replication on the
volume.
Total replica reserve is the amount of space reserved for the replica set within the configured delegated space on the
secondary group. Total replica reserve is a percentage of the current replica volume reserve that provides additional
space for replicas. If the current replica reserve is 1 GB, and you specify 200% for total replica reserve, the total replica
reserve size is 2 GB. If the current replica volume reserve increases to 4 GB, then the total replica reserve size also
increases to 8 GB. The total replica reserve for a volume can potentially limit the number of replicas that are kept. To
prevent older replicas from being deleted, space can automatically be borrowed from other sources when the total
replica reserve is consumed.
Figure 1 Examples of group space usage
For additional information on using Asynchronous Replication with Dell PS Series, refer to:
• Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
• Using Dell PS Series Asynchronous Replication
10 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
2 Best practices for space borrowing
For a system to gain the optimum benefit of space borrowing, apply the following best practices when planning and
configuring snapshot and replication storage space.
2.1 Planning space requirements
Space borrowing is intended to help during peaks of activity when additional space is needed temporarily. It does not
take the place of carefully provisioning reserves. For additional information on planning space requirements for
snapshots and replicas, refer to the following documents:
• Dell EqualLogic Group Manager Administrator’s Manual on eqlsupport.dell.com (login required)
• Dell PS Series Snapshots and Clones: Best Practices and Sizing Guidelines
• Using Dell PS Series Asynchronous Replication
2.2 Space borrowing prioritization
When necessary, the system automatically deletes a snapshot or replica that is borrowing space. Objects using
borrowed space are at risk for being deleted if the borrowed space is required to support another operation with a
higher priority. This could occur if a new snapshot of Volume A borrows snapshot reserve from Volume B and then
Volume B needs that space for its own snapshots.
Another example is space borrowed from free space in the storage pool that becomes needed to support the creation
of a new volume or expansion of an existing volume. This scenario could cause existing snapshots and replicas that are
borrowing the free space to be deleted. However, in-progress or last successful replicas are never deleted
automatically by this process.
2.3 Space borrowing behavior with changes to storage pools
If a volume or replica set is moved to another pool, the associated snapshots and replicas are bound to the space
borrowing limitations of the new pool. Also, if the size of a storage pool decreases due to the removal of a member,
this lowers the pool capacity as well as impacts the space borrowing capabilities.
2.4 Space borrowing for replication
While it is possible to enable or disable space borrowing for snapshots, space borrowing for replication is automatic
and cannot be disabled.
Remote replicas can borrow beyond their total replica reserve, but the total amount of configured reserve space must
still fit within the delegated space. If there is insufficient delegated space on the secondary group, the system requires
manual administrative intervention to increase the amount of delegated space.
11 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Also, if the replica reserve for a volume is configured with a very low value, such as the minimum 105%, the system can
potentially require manual administrative intervention to increase the reserve percentage so that an in-progress replica
can continue. In-progress replicas are not eligible to borrow space. See section 5.1.4 for details.
Note: To use space borrowing for replicas, all members in the secondary group must be running Dell PS Series
firmware version 8.0 or later. Space borrowing for snapshots requires Dell PS Series firmware v6.0 or later.
12 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
3 Space borrowing with thin provisioned volumes and SCSI UNMAP
Snapshot reserve is defined as a percentage of volume reserve. If the volume size changes, the snapshot reserve also
adjusts automatically. With thin provisioned volumes using SCSI UNMAP (with Microsoft Windows, VMware ESXi, or
Red Hat Linux) where the PS Series volume size shrinks as a result of data being deleted on the volume from the
operating system, snapshot reserve will also shrink. Without space borrowing enabled, this can potentially lead to older
snapshots being deleted, if the reserve space becomes entirely consumed.
Note: As a best practice, disable support for UNMAP from the operating system on hosts that are using Dell PS Series
volumes configured for replication (both asynchronous and synchronous).
13 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
4 Displaying borrowed space information
To view borrowed space information in the PS Series group:
1. In Group Manager, click Borrowed Space in the left pane.
You can also view space-borrowing statistics through several CLI commands. For additional information, refer to the
Dell EqualLogic Group Manager CLI Reference Guide at eqlsupport.dell.com (login required).
14 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
1. Local Space tab: Displays space borrowing information for the local PS Series group (section 4.1.1).
2. Remote Delegated Space tab: Displays space borrowing information for remote PS Series groups that are
replication partners (section 4.1.2).
1
2
15 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
4.1.1 Local Space tab
The Local Space tab displays space borrowing information for the local PS Series Group.
Callout
Description
A
Borrowed space by storage pool: This section summarizes borrowed space for the selected pool or all
pools.
B
Storage pool and resource column:
• Free space is the amount of unused space still available in the selected storage pool.
• Reserves are reserved space that can be borrowed and include snapshot reserve, local replication
reserve, and delegated space. Reserves do not include volume reserve or storage containers for
NAS or vVols.
C
Total column: Indicates the amount of space being used for each storage pool and resource including
snapshot and replica reserves, and free space. This data does not include volume reserves and storage
containers for NAS or vVols.
D
Used as designated column: Displays the amount of data that is consuming space within its own
reserve
E
Borrowed column: The total space that is being borrowed
F
Unused column: Denotes the amount of available space on each storage pool and resource
E
B
3
D
A
3
C
F
F
16 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Callout
Description
G
Object types in <selected pool> that can borrow space section: A summary of the space usage of
objects that can borrow space in the selected pool. Types of objects that can borrow space are:
• Snapshots
• Replica sets (inbound replicas in delegated space)
• Local replicas (outbound)
• Deleted volumes (in the Volume recovery bin)
H
Total reserves column: The amount of total reserve space allocated for each type of object
I
Total size column: The amount of space being used for each type of object
J
Reserves used column: The amount of reserve space being used for each type of object
K
Space borrowed column: The amount of space being borrowed for each type of object
J
G
3
K
3
H
3
I
3
17 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Callout
L
M
N
O
P
L
3
M
3
N
Q
3
P
3
18 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
4.1.2 Remote Delegated Space tab
The Remote Delegated Space tab displays space borrowing information for secondary groups that are replication
partners and summarizes the primary group delegated space usage at each replication partner.
The data is automatically updated each time the group communicates using a replication operation (such as enabling
replication on a volume or creating, modifying, or deleting a replica) with a replication partner. Remote actions on the
secondary group (such as deleting a replica) do not automatically trigger the GUI to be refreshed with new information.
However, the GUI can be manually refreshed to request an update.
Callout
A
B
C
D
E
F
G
A
B
C
D
E
F
G
19 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
Callout
H
I
J
K
L
M
N
O
I
J
K
L
M
N
O
H
20 Dell PS Series: Space Borrowing for Snapshots and Replicas | TR1084 | version 2
5 Space borrowing examples
5.1.1 Space borrowing with snapshots
In the following example, a 10 GB thick volume is configured with 100% (10 GB) of snapshot reserve.
As snapshot borrowing is enabled on the volume, it is possible for the snapshot space to exceed the configured 10 GB
snapshot reserve for the volume. In the example below, the full 10 GB of configured snapshot reserve space is being
used, two additional GB are borrowed from the storage pool. A total of 12 GB of snapshot space is used. If snapshot
space borrowing was not enabled, it would not be possible for the snapshot space to exceed the initially configured 10
GB limit.
Note: Because snapshot reserve is a percentage of the volume reserve, the amount of snapshot reserve space
fluctuates in direct proportion to a thin-provisioned volume reserve when data is dynamically written and deleted (for
example, when invoking SCSI UNMAP from Microsoft Windows, VMware ESXi or Red Hat Linux — see section 3).
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
Page is loading ...
  • Page 1 1
  • Page 2 2
  • Page 3 3
  • Page 4 4
  • Page 5 5
  • Page 6 6
  • Page 7 7
  • Page 8 8
  • Page 9 9
  • Page 10 10
  • Page 11 11
  • Page 12 12
  • Page 13 13
  • Page 14 14
  • Page 15 15
  • Page 16 16
  • Page 17 17
  • Page 18 18
  • Page 19 19
  • Page 20 20
  • Page 21 21
  • Page 22 22
  • Page 23 23
  • Page 24 24
  • Page 25 25
  • Page 26 26
  • Page 27 27
  • Page 28 28
  • Page 29 29
  • Page 30 30

Dell Enterprise Solution Resources Owner's manual

Dell
Brand
Dell
Model
Enterprise Solution Resources
Type
Owner's manual
This manual is also suitable for
Download PDF
report

Ask a question and I''ll find the answer in the document

Finding information in a document is now easier with AI

Related papers

Other documents