Disk read or write is too slow on Azure

Products

• VMware Tanzu Greenplum
• VMware Tanzu Data Suite
• VMware Tanzu Data Suite

Issue/Introduction

Disk read/write is too slow on Azure and Greenplum runs slow on Azure. This article will explain what to do when gpcheckperf shows very slow disk read/write speeds.

Environment

Greenplum on Azure

Resolution

Some customers may find that Greenplum runs slow on Azure. Running gpcheckperf would show read/write speed only at 100MB/s on the host disk.

This slow disk speed may be caused by the incorrect VM configuration (using single disk for each VM). We suggest that the customer add more disks for each VM.

Each disk has a throughput limit in addition to the Instance Type having a limit. For AWS and Azure, the disk limit is lower than the Instance Type limit so, in order to achieve the instance type limit you must use multiple disks per VM.
This also impacts the number of Segments because each segment is only in one directory.

• The number of Segments can not exceed the number of mounts.
• The number of Segments must be a multiple of the number of mounts For AWS, ST1 disks can reach the throughput limit of all tested Instance Types. The size of the ST1 disk also impacts performance. At 12.5TB, the ST1 performance is maximized.

Azure Notes:
Premium and Standard storage options (SSD and HDD) but Instance Types that support Premium storage have lower throughput limits.
More disks are needed per host than the Instance Type will support Segments (memory and CPU)
Software RAID 0 needed to reduce the number of mounts but Software RAID negatively impacts performance.
The larger the number of disks in software RAID, the worse the performance
The size of the disk impacts performance
For Azure, much more testing was needed to optimize each instance type than AWS or GCP. For GCP, disk performance is relatively very low for each instance type. The number and size of the disks does not impact throughput. The type of disk has a small impact on performance where SSD is slightly faster. The HDD performance of 120 MB/s write and 180 MB/s read means GCP can not handle very many Segments per host."