Database Reference
In-Depth Information
additional disks.
If you hot-add new disks and need to create new data files, SQL Server will stripe the
data to the newly created data files as they have the more free space. For this reason,
we recommend you add more than one virtual disk and data file to try and spread the IO
load. This will help avoid creating hot spots. The number of VMDKs and data files you
need to create will depend on your SQL workload profile.
Tip
Because the transaction log is written to sequentially and not striped, it is
recommended that the VMDK or RDM be extended if necessary, rather than hot-
adding a disk and creating a new log file. In vSphere 5.x, a VMDK can be
expanded online without disruption up to a maximum of 2TB-512 Bytes.
Jumbo VMDK Implications for SQL Server
vSphere 5.5 introduced the ability to provision 62TB Jumbo VMDKs and Virtual Mode
RDMs (vRDM) with a VM. Physical Mode RDMs (pRDM) are capable of being
provisioned up to 64TB, as of vSphere 5.0. The VMware maximum VMFS data store
size is 64TB, as it was in vSphere 5.0. This allows truly massive storage footprints to a
single VM.
With Virtual Hardware Version 10, we now have the ability to provision a single VM
with maximum storage capacity (see
Table 6.8
).
Table 6.8
Maximum Virtual Machine Storage
Just because the size of the virtual disk increases doesn't mean the performance of the
virtual disk increases. With each virtual disk, the queue depth is still the same
regardless of the size. This limits the parallelism of IOs to a single virtual disk, and it
will also limit the throughput unless SQL is issuing incredibly large IO sizes. For this
reason, the maximum capacity is largely theoretical because you would not be able to
get the necessary performance.
Tip
The maximum theoretical SQL 2012 database size is 524PB. The maximum data
