Apr 29, 2024
Other considerations – Addressing Disconnected Scenarios with AWS Snow Family
Let us assume the following conditions for a migration using an AWS Snowball Edge device:
A SAN array has two servers as clients
Each server utilizes two Logical Unit Numbers (LUNs) on the SAN
One server runs Windows Server 2019
One server runs Red Hat Enterprise Linux 8 (RHEL 8)
The Windows server exposes its data for copying through a CIFS share
The Linux server exposes its data using an NFS export
The desktop is going to act as a data mover for the AWS Snowball Edge device
Figure 4.9 – Hypothetical data movement paths
Looking at Figure 4.9, we can see several places where the throughput could get slowed down:
The disk groups/pools on the SAN array
The controllers/I/O ports on the SAN array
The Fibrechannel fabric connecting the SAN array to the servers
The hardware configuration of either server
The OS and file-serving configuration of either server
Whether either server is dedicated to this task or is running other apps
Differences in the CIFS and NFS protocols or their versions
The network between the servers and the desktop
Hardware and software configuration of the desktop
An even worse possibility is that the servers and the desktop can pull the data from the SAN at maximum speed of all devices and links involved, only to discover this causes the SAN controller to queue I/O requests for a third client you weren’t aware of.
It turns out this third server is running a large Microsoft SQL Server that consumes LUNs from the same disk pool on the SAN array, and it also shares the same pair of SAN controllers on the frontend. The 10 Gbit/s of sequential reads causes head thrashing on the disk pool and overruns the shared cache on the controllers.
As a result, the mission-critical application that depends on this database suffers performance degradation – or worse, an outage. Anyone who has overseen many data center migrations – to the cloud or otherwise – has probably witnessed such a situation. Figuring out how fast you can possibly move data onto a device is important, but it is even more important to determine the maximum non-impactive speed for the source of the data.
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