EC2 (local) instance storage
Posted Dec 9, 2012 12:04 UTC (Sun) by man_ls
In reply to: EC2 (local) instance storage
Parent article: Optimizing stable pages
When Amazon EC2 creates a new instance, it allocates a new instance storage with its own filesystem. This process includes formatting the filesystem, and sometimes copying files from the AMI (image file) to the new filesystem. So any previous filesystems are erased. It is here that zeroing unallocated blocks from the previous filesystem comes into place, which is what FALLOC_FL_NO_HIDE_STALE would mess up.
I don't know how Amazon (or the hypervisor) prevents access to the raw disk, where unallocated sectors might be found and scavenged even if the filesystem is erased. I guess they do something clever or we would have heard about people reading Zynga's customer database from a stale instance.
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