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I wanted to give a boost to one of my Azure virtual machines that is being used as a build server for processing thousands of small files in bursts. So I decided to add a small 32 GiB premium storage (SSD) disk.

But while reading Microsoft documentation for Azure disks, something puzzled me:

For a 32 GiB standard disk (S4):

IOPS per disk 500

Throughput per disk 60 MB/sec

For a 32 GiB premium disk (P4):

IOPS per disk 120

Throughput per disk 25 MB/sec

Does this mean that for small disks there is no point of upgrading to premium SSD because performance will be actually lower? It does not make logical sense to me. Is it true or I misunderstand something?

  • From what I've seen, you can achieve up to 80K iOPS per VM with premium storage. So it seems that the performance increases exponentially in this case. – B.J.Goodman Mar 8 '18 at 18:13
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Yes, the performance of standard storage is the same per disk across the board, whereas premium storage increases as the disk size increases. This does mean that for smaller premium disks the performance may be low than the same size standard disk.

The main reason you would use premium disk at this size is for the SLA. To be able to get the 99.9% SLA for single instance VM's then you must use premium disks. Generally premium storage is recommend for production work loads.

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Just to add to Sam Cogan's response, the SLA for single-instance VMs is covered here. Furthermore, Standard storage disks are subject to transaction costs, which Premium disks are not. That is covered on the pricing page.

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