The New and Improved Microsoft Hotmail Storage System

Microsoft has disclosed a new way that data storage will be handled on Hotmail. At the beginning this year a new system based on technologies developed at Hotmail has been running on a pilot cluster using personal accounts of Microsoft employees. And after rigorous testing the new system has been certified which provides better reliability at a significantly lower price.

Hotmail JBOD Architecture

The new Hotmail storage system is JBOD (Just a Bunch Of Disks). Copies of data resides on independent hard drives, controllers, and machines. Thus making the hard drive controller almost completely out of the way and handing it to software to control.

This JBOD software constantly monitors for failures and raises an alert when found thus triggering a repair process. This repair process can be rebooting a machine or restarting a process, to fixing data corruption or even involving human intervention if required. The main advantage of using Software is it can maintain the good copies of mails prioritizing repair action if it finds less copies. Using this software, replication itself was simplified

Formerly, Hotmail has been using RAID (Redundant Array of Inexpensive Disks). Emails were kept on multiple RAID groups so that even when entire RAID fails, messages can be restored. Hotmail studied the reliability perspective of drives of capacity larger than 1 terabyte and found that it was not money’s worth from the reliability point of view.

Hotmail RAID Architecture

As RAID systems easily deals with problems affecting single system but not when whole machine or the RAID controller runs into problems. Hotmail found that having copies on a different machine not sharing the controller was not only more reliable but cost wise also less expensive than RAID configuration.

Microsoft, in the Windows Team blog post,  also revealed that Hotmail will also add solid state drives to handle other functions. SSDs are much faster than normal hard drives but are also much more expensive.

Hotmail SSD Architecture

The new Hotmail storage system will use SSDs to handle features like “the list of messages in your inbox, read/unread status of your messages, conversation threading, mobile phone synchronization etc.

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