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Method and Program to Dynamically Change Storage Devices in a Backup System Disclosure Number: IPCOM000126849D
Original Publication Date: 2005-Aug-02
Included in the Prior Art Database: 2005-Aug-02
Document File: 2 page(s) / 71K

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System to Handle Metadata Requests for Global Data Devices Efficiently During a Reassign

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Method and Program to Dynamically Change Storage Devices in a Backup System

A system exists called Global Data (GD), where a service is provided for clients in the Storage Subsystem (SS) to store vital data called metadata in multiple copies on Storage Devices (SD). This data is critical to the normal operations of the SS, where individual reads/writes cannot be failed back to clients unless access is lost to all copies of the GD. This task becomes difficult during SD failures, where a process known as a Reassign selects a new SD and places a copy of the GD on it. The System described here is a method to successfully Reassign without failing individual metadata requests, and to restore I/O access to metadata blocks as soon as possible.

The figure shows a SS connected to three SDs, where each SD contains a complete copy of GD. A copy of GD on a SD is divided into Metadata Blocks (MB), which are grouped into areas reserved for each client to store their metadata. Clients in a SS may send multiple Client Requests (CR) to read/write their metadata. Each CR is multiplied into three Device Transactions (DT), one for each GD SD (ie, a CR_1 is multiplied into DT_1a on the Primary SD, DT_1b on the Secondary SD, and DT_1c on the Tertiary SD). At the successful completion of the three parallel DTs, the CR is returned with success to the client.


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During a Reassign when a SD is failing, all GD I/O is stopped...