Managing Storage

XenServer storage repositories (SR) are storage containers on which virtual disks are stored. Both storage repositories and virtual disks are persistent, on-disk objects that exist independently of XenServer. SRs can be shared between servers in a resource pool and can exist on different types of physical storage device, both internal and external. These devices include local disk devices and shared network storage. Various different types of storage are available when you create a storage repository using the New Storage Repository wizard. Depending on the type of storage selected, several advanced storage features can be configured in XenCenter. These features include:

  • Dynamic multipathing. On Fibre Channel and iSCSI SRs, you can configure storage multipathing using round robin mode load balancing. For more information, see Storage Multipathing.

  • Thin provisioning. On NetApp and Dell EqualLogic SRs, you can choose the type of space management used.

    By default, allocated space is thickly provisioned and all virtual allocation guarantees are fully enforced on the filer. This behavior guarantees that virtual disks never run out of space and therefore experience failed writes to disk.

    Thin provisioning allows the disks to be better utilized, as physical capacity is allocated only as a VM needs it - when it writes. This behavior allows for over provisioning of the available storage and maximum utilization of your storage assets.

  • Reclaiming Freed Space. On a thinly provisioned block-based SR, you can free up unused space (for example, deleted VDIs in a LUN). The storage repository can then reuse the reclaimed space. For more information, see Reclaiming Freed Space.

  • Live LUN Expansion. Live LUN Expansion enables you to increase the size of the LUN without any VM downtime. For more information, see Live LUN Expansion.

When you configure a server or pool, you nominate a default SR which is used to store crash dump data and images of suspended VMs. This SR is the default SR used for new virtual disks. At pool level, the default SR must be a shared SR. Any new virtual disks, crash dump files or suspended VM images created within the resource pool are stored in the pool’s default SR. This behavior provides a mechanism to recover from physical server failure. For standalone servers, the default SR can be local or shared. When you add shared storage to a standalone server, the shared storage automatically becomes the default SR for that server.

It is possible to use different SRs for VMs, crash dump data and suspended VM using XenServer xe CLI. For more information, see Command line interface.

Managing Storage

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