Abstract: A hybrid storage array one using two or more storage device tiers. In one implementation, two tiers may be provided by solid state drives (SSDs) and hard disk drives (HDDs). Host application access patterns of a certain type determined to be relatively slow, such as random writes, are detected. The random writes are collected and written to a special reserve space, such as a portion of the SSD storage tier, referred to as a write cache extension. The write cache extension absorbs such accesses that would otherwise be written to HDD storage directly. Data structures are created in a cache memory local to an array controller representing the location on SSD reserve space to which the writes were committed and a location in the storage system where they were originally intended to go. The write cache extension can be enabled all of the time, or only when the array controller write cache experiences certain operating conditions, such as when its utilization exceeds a certain predetermined amount.

Abstract: A hybrid storage array one using two or more storage device tiers. In one implementation, two tiers may be provided by solid state drives (SSDs) and hard disk drives (HDDs). Host application access patterns of a certain type determined to be relatively slow, such as random writes, are detected. The random writes are collected and written to a special reserve space, such as a portion of the SSD storage tier, referred to as a write cache extension. The write cache extension absorbs such accesses that would otherwise be written to HDD storage directly. Data structures are created in a cache memory local to an array controller representing the location on SSD reserve space to which the writes were committed and a location in the storage system where they were originally intended to go. The write cache extension can be enabled all of the time, or only when the array controller write cache experiences certain operating conditions, such as when its utilization exceeds a certain predetermined amount.

Abstract: Techniques for detection of impending data errors in a mass storage system, such as a track squeeze problem in an electromagnetic disk drive, and then repairing the impending problem, such as by rewriting the affected tracks. In many cases the problem is detected and repair is effected when the original data can still be read. In other cases, when the data is no longer readable on the disk in question, but when the disk is part of a Redundant Array of Independent Disks (RAID) system, or other system in which higher layer fault tolerance mechanisms are implemented, the missing data can be recovered via these mechanisms. The recovered data is then used to repair the track squeeze problem. The invention can be implemented as firmware in a storage system, as a component of a general purpose operating system, or inside individual disk drives, or it can use a combination of these implementations.