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Figure 24.

The sample environment

Configuring for high availability

After virtualizing physical servers that had been dedicated to particular applications and
consolidating the resulting VMs on a XenServer host, you must ensure that the host will be able to run
these VMs. Designing for high availability means that the components of this environment – from
servers to storage to infrastructure – must be able to fail without impacting the delivery of associated
applications or services.

For example, HP StorageWorks P4000 SANs offer the following features that can increase
availability and avoid SPOFs:



Hardware-based RAID for the storage node



Multiple network interfaces bonded together

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Summary of Contents for LeftHand P4000 - SAN Solutions

Page 1: ...orage node 7 Clustering and Network RAID 8 Networking bonding 8 Configuring an iSCSI volume 9 Example 9 Creating a new volume 10 Configuring the new volume 11 Comparing full and thin provisioning 12 Benefits of thin provisioning 12 Configuring a XenServer Host 13 Synchronizing time 14 NTP for XenServer 15 Network configuration and bonding 16 Example 17 Connecting to an iSCSI volume 19 Determining ...

Page 2: ... multiple clusters 41 Disaster recoverability 45 Backing up configurations 46 Resource pool configuration 46 Host configuration 46 Backing up metadata 47 SAN based Snapshots 48 SAN based Snapshot Rollback 49 Reattach storage repositories 50 Virtual Machines VMs 51 Creating VMs 51 Size of the storage repository 51 Increasing storage repository volume size 52 Uniqueness of VMs 53 Process preparing a...

Page 3: ...lustering network RAID thin provisioning snapshots remote copies cloning performance monitoring and a single pane of glass management can add value in your environment This paper explores options for configuring and using XenServer with emphasis on best practices and tips for an HP StorageWorks P4000 SAN environment Target audience This paper provides information for XenServer Administrators inter...

Page 4: ...impact of a site failure Snapshots can prevent data corruption when you are rolling back to a particular point in time Remote snapshots can be used to add sources for data recovery Comprehensive cost effective capabilities for high availability and disaster recovery DR applications are built into every HP StorageWorks P4000 SAN There is no need for additional upgrades simply install a storage node...

Page 5: ...w HP StorageWorks P4000 SAN A SAN can be defined as an architecture that allows remote storage devices to appear to a server as though these devices are locally attached In an HP StorageWorks P4000 SAN implementation data storage is consolidated on a pooled cluster of storage nodes to enhance availability resource utilization and scalability Volumes are allocated to XenServer hosts via an Ethernet...

Page 6: ...r that describes how XenServer hosts find and connect to an SR Virtual block device A virtual block device VBD is a connector that describes how a VM connects to its associated VDI which is located on a SR Overview of XenServer iSCSI storage repositories XenServer hosts access HP StorageWorks P4000 iSCSI storage repositories SRs either using the open iSCSI software initiator or thru an iSCSI Host ...

Page 7: ...ble to consolidate data Storage reallocation can be achieved without cabling changes In much the same way that XenServer can be used to efficiently virtualize server resources HP StorageWorks P4000 SANs can be used to virtualize and consolidate storage resources while extending storage functionality Backup and DR are also simplified and enhanced by the ability to move VM data anywhere an Ethernet ...

Page 8: ...rfaces into a single logical interface Bonding supports path failover in the event of a failure in addition depending on the particular options configured bonding can also enhance throughput In its basic form a network bond forms an active passive failover configuration that is if one path in this configuration were to fail the other would assume responsibility for communicating data Note Each net...

Page 9: ... using the Centralized Management Console CMC In this example the HP Boulder management group defines a single storage site for a XenServer host resource pool farm or a synchronously replicated stretch resource pool HP Boulder can be thought of as a logical grouping of resources A cluster named IT DataCenter contains two storage nodes v8 1 01 and v8 1 02 20 volumes have currently been created This...

Page 10: ...10 Figure 2 Using CMC to obtain detailed information about volume XPSP2 01 Creating a new volume The CMC is used to create volumes such as XPSP2 01 as shown in Figure 3 ...

Page 11: ...orage and will be discussed later in the Configuring a XenServer Host section Configuring the new volume Network RAID 2 Way replication is selected to enhance storage availability now the cluster can survive at most one non adjacent node failure Note The more nodes there are in a cluster the more nodes can fail without XenServer hosts losing access to data Thin Provisioning has also been selected ...

Page 12: ...olume within the storage cluster Thin Provisioning With Thin Provisioning you reserve less space in the storage cluster than that presented to XenServer hosts Thus when a thinly provisioned 10GB volume is created only 1GB of space is initially reserved for this volume however a 10GB volume is presented to the host If you were also to select 2 Way Replication 2GB of space 1 GB x 2 would initially b...

Page 13: ...rotocol SNMP triggers or CMC storage monitoring so that you can initiate an effective response prior to a full cluster event Should a full cluster event occur writes requiring additional space cannot be accepted and will fail until such space is made available effectively forcing the SR offline In order to increase available space in a storage cluster you have the following options Add another sto...

Page 14: ...re configured to use local time for time stamping operations Alternatively a network time protocol NTP server can be used to manage time for a management group rather than relying on local settings Since XenServer hosts VMs applications and storage nodes all utilize event logging it is considered a best practice particularly when there are multiple hosts to synchronize time for the entire virtuali...

Page 15: ...r Although NTP Server configuration may be performed during a XenServer installation the console may also be used post installation Within XenCenter highlight the XenServer and select the Console tab Enable NTP using xsconsole Enable NTP as shown in Figure 6 ...

Page 16: ...terface which not only provides redundant paths but also increases the bandwidth for SRs If desired you can create an additional bond for LAN connectivity Note XenServer supports source level balancing SLB bonding It is a best practice to ensure that the network adapters configured in a bond have matching physical network interfaces so that the appropriate failover path can be configured In additi...

Page 17: ...sure there are no VMs running on the particular XenServer host 2 Select the host in XenCenter and open the Network tab as shown in Figure 7 A best practice for the networks is to add a meaningful description to each network in the description field Figure 7 Select host in XenCenter and open Network tab 3 Select the NICs tab and click the Create Bond button Add the interfaces you wish to bond as sh...

Page 18: ...dy been bonded to form a single logical network link for Ethernet traffic The network in this example consists of a class C subnet of 255 255 255 0 with a network address of 1 1 1 0 No gateway is configured IP addressing is set using the pif reconfigure ip command 4 As shown in Figure 9 select Properties for each bonded network rename Bond 2 3 to Bond 0 and rename Bond 4 5 to Bond 1 and enter appr...

Page 19: ... a one to one relationship with one rule for one host CHAP Challenge Handshake Authentication Protocol CHAP provides a mechanism for defining a user name and secret password credential to ensure that access to a particular iSCSI volume is appropriate Think of this as a one to many relationship with one rule for many hosts XenServer hosts only support one way CHAP credential access Determining or c...

Page 20: ...20 Figure 10 Determining the IQN of a particular XenServer host If desired you can use the General tab s Properties button to change the host s IQN as shown in Figure 11 ...

Page 21: ...sally Unique Identifier UUID must be specified Verify the change using the host param list command Specifying IQN authentication This subsection talks about an authentication method that is given a name Before specifying the authentication method for a volume you can use the CMC to determine its IQN In this example SR access is created for volume XPSP2 01 which has an IQN of iqn 2003 10 com leftha...

Page 22: ...er highlight the Servers 0 selection Note that the currently defined authentication rule method is currently zero 0 2 To obtain the New Server dialog box as shown in Figure 13 either right click on Servers 0 and select New Server Select Server Tasks New Server or utilize Tasks Server New Server ...

Page 23: ... 06 com example e834bedd in the Initiator Node Name field 4 After you have created the XenServer 55b 02 you can assign volumes and snapshots Under the Volumes and Snapshots tab select Tasks Assign and Unassign Volumes Snapshots Alternatively select Tasks Volume Edit Volume Selecting the Volume Basic tab Assign and Unassign Servers The former option focuses on assigning volumes and snapshots to a p...

Page 24: ...24 Figure 14 Assigning volumes and snapshots to server XenServer 55b 02 Figure 15 Assigning servers to volume XenServer 55b 02 ...

Page 25: ... 55b 02 is 1 1 1 230 the virtual IP address of the HP StorageWorks iSCSI SAN cluster is 1 1 1 225 Use the following procedure to create a shared LVM SR 1 In XenCenter select Storage Repository or with XenCenter 5 5 New Storage 2 Under Virtual disk storage select iSCSI to create a shared LVM SR as shown in Figure 16 Select Next Figure 16 Selecting the option to create a shared LVM SR 3 Specify the ...

Page 26: ...iSCSI SAN cluster Next select Discover IQNs to list visible iSCSI storage targets in a drop down list Match the Target IQN value to the IQN of volume XPSP2 01 as shown in the CMC Select Discover LUNs then specify LUN 0 as the Target LUN forcing iSCSI to be presented at LUN 0 for each unique target IQN Select Finish to complete the creation of the new SR ...

Page 27: ...ore being presented to the XenServer host for use as VM storage As shown in Figure 19 any data on a volume that is not in an LVM format will be lost during the format operation After the format is complete the SR will be available and enumerated in XenCenter under the XenServer host as shown in Figure 20 ...

Page 28: ... VM on the SR you have just created 1 From XenCenter s top menu select VM New 2 Select the desired operating system template for the new VM In this example the VM will be running Microsoft Windows XP SP2 3 For consistency specify the VM s name as XPSP2 01 as shown in Figure 21 Figure 21 Naming the new VM 4 Select the type of installation media to be used either Physical DVD Drive used in this exam...

Page 29: ...efore its deployment in a live environment 6 Increase the size of the virtual disk from 8GB default to 9GB as shown in Figure 22 While the iSCSI volume is 10GB some space is consumed by LVM SR overhead and is not available for VM use Note The virtual disk presented to the VM is stored on the SR Figure 22 Changing the size of the virtual disk presented to the VM 7 Allocate a single network interfac...

Page 30: ...AN An HP StorageWorks P4000 SAN was configured as a cluster of two storage nodes A virtualized 10GB iSCSI volume XPSP2 01 was configured with Network RAID and allocated to the host A XenServer SR XPSP2 01 was created on the iSCSI volume A VM XPSP2 01 with Windows XP SP2 installed was created on a 9GB virtual disk on the SR Figure 24 outlines this configuration which can be managed as follows The X...

Page 31: ...t will be able to run these VMs Designing for high availability means that the components of this environment from servers to storage to infrastructure must be able to fail without impacting the delivery of associated applications or services For example HP StorageWorks P4000 SANs offer the following features that can increase availability and avoid SPOFs Hardware based RAID for the storage node M...

Page 32: ...lure XenServer resource pools can be configured as a stretch cluster across multiple sites with HP StorageWorks P4000 SANs maintaining multi site synchronously replicated SAN volumes that can be accessed at these same sites Enhancing infrastructure availability The infrastructure that has been configured in earlier sections of this white paper shown in Figure 24 has an SPOF the network switch By a...

Page 33: ...Works P4000 SAN bonds You must configure the networking bonds for adaptive load balancing ALB Dynamic LACP 802 3ad cannot be supported across multiple switch fabrics XenServer host bonds SLB bonds can be supported across multiple switches Implementing Network RAID for SRs HP StorageWorks P4000 SANs can enhance the availability of XenServer SRs The resiliency provided by clustering storage nodes wi...

Page 34: ... You can set the Network RAID configuration for a particular volume either during its creation or by editing the volume s properties on the Advanced tab as shown in Figure 27 You can update Network RAID settings at any time without taking the volume down The following Network RAID options are provided 2 Way Up to one adjacent node failures in a cluster as seen above 3 Way Up to two adjacent node f...

Page 35: ...s a single entity with shared resources as shown in Figure 28 A pool of up to 16 XenServer hosts can be used to run and manage a large number of VMs Figure 28 A XenServer host resource pool with two host machines Key to the success of a host resource pool is the deployment of SAN based shared storage providing each host with equal access that appears to be local With shared storage VMs can be conf...

Page 36: ...igure HA using the Configure HA wizard Creating a heartbeat volume Since XenServer HA requires a heartbeat mechanism within the SR you should create a special HP StorageWorks iSCSI volume for this purpose This heartbeat volume must be accessible to all members of the resource pool and must have a minimum size of 356MB It is a best practice to name the heartbeat volume after the resource pool addin...

Page 37: ...d in the pool Options include Protect The Protect setting ensures that HA has been enabled for VMs Protected VMs are guaranteed to be restarted first if sufficient resources are available within the pool Restart if possible VMs with a Restart if possible setting are not guaranteed to be restarted following a host failure However if sufficient resources are available after protected VMs have been r...

Page 38: ...p resources you must first disable its HA protection Unless HA is disabled shutting down a protected VM would trigger a restart You can also specify the number of server failures to be tolerated Figure 31 Configuring resource pool HP Boulder IT for HA XenCenter provides a configuration event summary under the resource pool s Logs tab Following the HA configuration you can individually tailor the s...

Page 39: ... site SRs must be synchronously replicated and made available at each site HP StorageWorks P4000 SANs support this scenario by allowing you to create a divided replicated SAN cluster known as a multi site SAN as shown in Figure 32 Note Since storage is being simultaneously replicated to both sites you should ensure that appropriate bandwidth is available on the SAN Figure 32 Sample stretch pool co...

Page 40: ...on This requirement is straightforward in a two node cluster however with a four node cluster you would deploy nodes 1 and 3 at Site A while deploying nodes 2 and 4 at Site B With the four node cluster volumes must at a minimum be configured for Replication Level 2 thus even if Site A or B were to go down storage nodes at the surviving site can still access the volumes required to support local VM...

Page 41: ...ld constantly need to transfer pool status and management information across the network a stretch pool would be impractical in this case Instead you should create separate resource pools at each site as shown in Figure 34 Figure 34 Editing the cluster In the implementation shown in Figure 34 the remote site would be utilized in the event of the complete failure of the primary site Site A Resource...

Page 42: ...s based on the following criteria Rate at which data changes Amount of bandwidth available Tolerability for data loss following a site failure Remote snapshots can be performed sub hourly or less often daily weekly These asynchronous snapshots provide a mechanism for recovering VMs at a remote site In any HA environment you must make a business decision to determine which services to bring back on...

Page 43: ...of Remote XPSP2 02 8 Set the retention policy for the remote site Depending on the scheduled start time replication may now commence The first remote snapshot copies all your data perhaps many terabytes to the remote cluster To speed up the process you can carry out this initial push on nodes at the local site then physically ship these nodes to the remote site6 For more information refer to the s...

Page 44: ...n then be started with the remote volume snapshots For more information on this process refer to Changing the Storage Repository and Virtual Disk UUID Note If Site A is down while the remote site is running the VMs there is no need to change UUIDs Changing the direction of snapshots As shown in Figure 38 after Site A has been restored change the direction of remote snapshots to resynchronize snaps...

Page 45: ...environment just as easily as in a physical environment you must predetermine restoration points that are tolerable to your business goals along with the data you need to protect You must also specify the maximum time it can take to perform a restoration which is effectively downtime it may be critical for your business to minimize this restoration time This section outlines different approaches t...

Page 46: ...storing the resource pool configuration In a restoration operation the dry run parameter can be used to ensure you are able to perform a restoration on the desired target For the restoration to be successful the number of network interfaces and appropriately named NICs must match the resource pool at the time of backup The following curl command can be used to transfer files from a server to a Fil...

Page 47: ...ors virtual disks stored on these SRs are connected to VMs by virtual block device VBD descriptors These descriptors can be thought of as SR level VM metadata that provide the mechanism for associating physical storage to the XenServer host and for connecting VMs to virtual disks stored on the SR Following a disaster the physical SRs may be available however you need to recreate the XenServer host...

Page 48: ...ase of thinly provisioned snapshots by only utilizing delta changes from writes to the original volume In addition snapshots and multiple levels of snapshots do not affect XenServer host efficiency to the original iSCSI volume unlike snapshots originating from within XenServer Hosts on LVM over iSCSI volumes Also snapshots may be scheduled with retention schedules for local clusters or even sent t...

Page 49: ...from the source XenCenter snapshot will be required as a recovery step The Storage Repository s iSCSI volume will be selected as the source for the snapshot In this example the VM XPSP2 05 is shut down Highlight the XPSP2 05 volume in the CMC right click and select New Snapshot as shown in Figure 42 The Default Snapshot Name of XPSP2 05_SS_1 will be pre populated and by default no servers will be ...

Page 50: ...ck to the previous state and the connection is re established to the rolled back volume The virtual machine may once again be restarted and will start in the state as represented by the iSCSI volume at the time of the original snapshot See Figure 44 Figure 44 Snapshot rollback continued Reattach storage repositories For new XenServer Hosts or resource pools recovering Storage Repositories a specia...

Page 51: ...In this manner it is clear which VM is contained within which virtual disk on a storage repository stored on which iSCSI volume In planning for VM Storage Repository use certain best practices must be followed for iSCSI LVM supported volumes An LVM over iSCSI volume may contain many virtual disks however it is considered best practice and best performance to allocate a single storage repository to...

Page 52: ...eeded volume the administrator may be able to prolong changing storage allocations and thereby save future administrative actions and thereby save time Increasing storage repository volume size HP StorageWorks P4000 volumes may be edited at any time and volume size increased to accommodate future needs In order to have an increase in volume size be recognized by XenServer hosts and ultimately VMs ...

Page 53: ...rom another On networks each NIC has a unique MAC address and each a unique IP address Within a domain each machine a unique host name Within Windows networks each Windows machine caries a unique Security Identifier SID Within XenServer hosts or resource pools each storage repository contains a unique UUID With each storage repository each virtual disk also contains a unique UUID The purpose of ea...

Page 54: ...eation of Storage Repositories and virtual disks on those repositories thereby not requiring changes to their UUID Changing the Storage Repository and Virtual Disk UUID A universally unique identifier UUID is used to identify objects inside a XenServer host or resource pool For storage repositories this identifier is created upon creation of a storage repository and allows one SR to be uniquely id...

Page 55: ...ver Hosts in the resource pool are assigned read write access to the volume In the CMC highlight the XPSP2 02 RS 1_RS_1 remote snapshot right click on that snapshot and select Delete Snapshot A stand alone primary iSCSI volume XPSP2 02 RS 1 now exists which is a complete copy of the original XPSP2 02 volume data storage repository virtual disk and UUIDs in all Since only one unique UUID may be pre...

Page 56: ...a7f4d6 75c7 8318 6679 eb6702b11de1 Step 5 From the XenServer console in XenCenter The XPSP2 02 RS 1 storage repository physical volume attributes mapped to device path dev sdd is now changed Note that the appropriate device path value must be used from what was found in Step 3 On the console command line type pvchange uuid dev sdd The command should return that the physical volume dev sdd changed ...

Page 57: ...lid to use Either by random selection or manual choice a unique UUID must be used The format of the renamed command will append VG_XenStorage to the start of the UUID On the console command line type vgrename VG_XenStorage 13a7f4d6 75c7 8318 6679 eb6702b11de1 VG_XenStorage da304b0f fe27 40b2 9034 7799b97b197d The command returns that the volume group VG_XenStorage 13a7f4d6 75c7 8318 6679 eb6702b11...

Page 58: ...enamed Two random UUIDs will be created with the following command cat proc sys kernel random uuid cat proc sys kernel random uuid The command returns two random UUIDs In this example the two random UUIDs are 1a1ccad1 5528 4809 8c3c 28665474364b and 94d23675 8e6a 460e 998a 04c0adbb47dd On the console command line type each command separately lvrename dev VG_XenStorage da304b0f fe27 40b2 9034 7799b...

Page 59: ...ta from the replication Note the new UUID of the storage repository Do not select format otherwise the VM and data on the volume will be lost The XPSP2 02 RS 1 volume will now be attached and seen to the XenServer resource pool Figure 51 Volume now attached to the XenServer Resource Pool Step 12 In the XenCenter Console select New VM Select the template appropriate for the cloned VM on the XPSP2 0...

Page 60: ... ready to be started SmartClone the Golden Image VM HP StorageWorks P4000 SAN SmartClone volumes are space efficient copies of existing volumes or snapshots that are created instantaneously and are fully featured writeable volumes SmartCloned volumes share the initial volume space By creating a sysprep VM and using the SmartClone process you instantaneously create multiple volumes with access to t...

Page 61: ...pace occupying only what is newly written in its space on the SAN Note that each iSCSI volume is addressed thru its own IQN just like a regular volume Since SmartClones are based from a source snapshot each VM is now managed as a single VM entity If single point patch management is required the original VM s volume must be patched and new SmartClone VMs must be recreated A single base snapshot can...

Page 62: ...space Functions such as defragmentation at the file system level may count as additional new writes to the SAN as some operating systems prefer to write new blocks over claiming original blocks Therefore it is considered best practice to defragment before a SmartClone is performed SmartClone volumes should disable defragmentation operations as this may lead to volumes filling out their thin provis...

Page 63: ...x HP Solution Centers http www hp com products1 solutioncenters jumpid go solutioncenters To help us improve our documents please provide feedback at http h20219 www2 hp com ActiveAnswers us en solutions technical_tools_feedback html Technology for better business outcomes Copyright 2010 Hewlett Packard Development Company L P The information contained herein is subject to change without notice Th...

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