Snapshot: Part Deux

Blog Post created by chheda Employee on Jan 30, 2013

This is the second blog in the two-part series on snapshots. Read part one covering the different implementations for snapshots and previous blog posts here.


In this post we’ll talk the concept of data integrity and highlight some of the videos on application integration with Nimble Storage.  Data is very valuable and any data loss can be catastrophic. Since snapshots are intended to be a backup of data, it is very important to preserve data correctly.


In addition to RAID, storage systems often use checksums to ensure data integrity is maintained. Nimble Storage’s CASL architecture goes further. First all data stored on disk by CASL is protected using a high performance version of RAID-6 (dual parity RAID). Next a checksum is also calculated and stored along with every block of data written to the array and a self-description of the block. The check sum and self-description is verified as the block is read. This ensures that data stored by CASL including snapshots is correctly preserved on the Nimble Storage array.


Continuing on the topic of checksum … like the data stored on disks, data cached in the SSDs is also check summed. This check sum is validated before sending the data to the host. If there is a mismatch, the data in cache is discarded and re-read from disk. The benefit of this is that all SSDs are used for caching and not spent on parity.


In addition to ensuring data is correctly stored and preserved; it is important to be able to take consistent backups of virtual machines and applications. This greatly simplifies recovery as everything is backed-up in a known state. Taking application and VM consistent snapshots is accomplished by integrating with framework such as Microsoft Volume Shadow Service (VSS). Nimble Storage customers are leveraging the Nimble Protection Manager functionality as well as integration with VMware vCenter to take application and VM consistent snapshots.


Here are a few videos and blogs that talk about application integration and more specifically Nimble Storage’s integration with applications.



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