Techniques for optimizing I/O operations

1. A method of processing I/O operations comprising:

receiving, at a storage appliance from a host, a plurality of read operations directed to a logical device having its data replicated on a plurality of data storage systems, wherein the storage appliance virtualizes storage resources of the plurality of data storage systems by presenting the storage resources to the host as a single pool of storage;

sending, by the storage appliance, the plurality of read operations to a first of the plurality of data storage systems;

detecting, by the storage appliance, that the plurality of read operations form a sequential read pattern of consecutive reads directed to consecutive logical addresses of the logical device;

identifying, by the storage appliance, a plurality of next sequential logical addresses of the sequential read pattern of the logical device;

receiving, at the storage appliance from the host, a sequence of subsequent reads directed to the next sequential logical addresses of the sequential read pattern of the logical device;

determining, in accordance with one or more criteria, a set of the plurality of data storage systems that are candidates to perform processing for the sequence of subsequent reads, wherein the one or more criteria include information describing current configuration options of the plurality of data storage systems affecting I/O operation performance, said one or more criteria including, for each of the plurality of data storage systems for which the storage appliance virtualizes storage resources, an indication regarding whether said each data storage system performs sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the set includes the first data storage system and a second of the plurality of data storage systems, and wherein the criteria indicates that both the first data storage system and the second data storage system for which the storage appliance virtualizes storage resources perform sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the first data storage system includes a first data cache used by the first data storage system and not used by the second data storage system, the second data storage system includes a second data cache used by the second data storage system and not used by the first data storage system, a first copy of the logical device is stored on physical devices of the first data storage system, and a second copy of the logical device is stored on physical devices of the second data storage system;

determining that the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system;

responsive to determining the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system, sending, by the storage appliance, the sequence of subsequent reads to the first data storage system but not the second data storage system; and

servicing, by the first data storage system, the sequence of subsequent reads using prefetched data stored in the first data cache.

2. The method of claim 1 , wherein the one or more criteria include an indication regarding whether each of the plurality of data storage systems performs data storage optimizations.

3. The method of claim 2 , wherein each data storage system in the set includes a plurality of storage tiers, each of the plurality of storage tiers having physical storage devices with performance characteristics that differ from other performance characteristics of other physical storage devices of other ones of the plurality of storage tiers, and wherein the data storage optimizations are performed on said each data storage system by a data storage optimizer of said each data storage system, and wherein the data storage optimizations include automatically relocating data portions among the plurality of storage tiers in accordance with an I/O workload associated with each of the data portions.

4. The method of claim 1 , wherein the current configuration options of the plurality of data storage systems described by the one or more criteria impact performance of I/O operations received subsequent to the plurality of read operations.

5. The method of claim 3 , wherein the logical device has a logical address space divided into a plurality of partitions and wherein the storage appliance performs first processing comprising:

collecting I/O workload information for each of the plurality of partitions regarding I/O operations having a target location in said each partition;

analyzing the I/O workload information for each of the plurality of partitions;

determining, in accordance with said analyzing, one or more of the plurality of partitions having a current I/O workload exceeding a specified threshold; and

sending a second plurality of read operations reading data from a location on the logical device located in a first of the one or more of the plurality of partitions to a same one of the plurality of data storage systems.

6. The method of claim 5 , wherein the specified threshold approximates a promotion threshold used by the data storage optimizer of the same one of the plurality of data storage systems to promote a data portion to a particular one of the plurality of storage tiers.

7. The method of claim 3 , further comprising:

sending one or more additional read operations to each of the first data storage system and the second data storage system, the first data storage system servicing the one or more additional read operations and returning requested read data, and wherein the second data storage system does not retrieve the requested read data from physical storage and does not return the requested read data, said second data storage system simulating one or more aspects of performing the one or more additional read operations, said one or more aspects including any of simulating cache contents and cache-related information to reflect having performed the one or more additional read operations and simulating generating updated I/O workload information to reflect having performed the one or more additional read operations, wherein the updated I/O workload information is used by the data storage optimizer of the second data storage system to determine placement of data portions on different ones of the plurality of storage tiers of the second data storage system.

8. The method of claim 3 , further comprising:

sending one or more additional read operations to each of the first data storage system and the second data storage system, each of the first data storage system and the second data storage system collecting I/O workload information for data portions of the logical device whereby the I/O workload information is used by the data storage optimizer of said each data storage system to locate data portions having highest I/O workload to a flash storage tier of the plurality of storage tiers of said each data storage system, at least some data portions of the logical device being located on the flash storage tier of said each data storage system, and wherein the method further includes:

detecting failure of one of the first and the second data storage systems; and

subsequent to the failure, sending all I/O operations directed to the logical device to the other of the first and the second data storage systems.

9. A system comprising:

a processor; and

a memory comprising code stored thereon that, when executed, performs a method of processing I/O operations comprising:

receiving, at a storage appliance from a host, a plurality of read operations directed to a logical device having its data replicated on a plurality of data storage systems, wherein the storage appliance virtualizes storage resources of the plurality of data storage systems by presenting the storage resources to the host as a single pool of storage;

sending, by the storage appliance, the plurality of read operations to a first of the plurality of data storage systems;

detecting, by the storage appliance, that the plurality of read operations form a sequential read pattern of consecutive reads directed to consecutive logical addresses of the logical device;

identifying, by the storage appliance, a plurality of next sequential logical addresses of the sequential read pattern of the logical device;

receiving, at the storage appliance from the host, a sequence of subsequent reads directed to the next sequential logical addresses of the sequential read pattern of the logical device;

determining, in accordance with one or more criteria, a set of the plurality of data storage systems that are candidates to perform processing for the sequence of subsequent reads, wherein the one or more criteria include information describing current configuration options of the plurality of data storage systems affecting I/O operation performance, said one or more criteria including, for each of the plurality of data storage systems for which the storage appliance virtualizes storage resources, an indication regarding whether said each data storage system performs sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the set includes the first data storage system and a second of the plurality of data storage systems, and wherein the criteria indicates that both the first data storage system and the second data storage system for which the storage appliance virtualizes storage resources perform sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the first data storage system includes a first data cache used by the first data storage system and not used by the second data storage system, the second data storage system includes a second data cache used by the second data storage system and not used by the first data storage system, a first copy of the logical device is stored on physical devices of the first data storage system, and a second copy of the logical device is stored on physical devices of the second data storage system;

determining that the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system;

responsive to determining the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system, sending, by the storage appliance, the sequence of subsequent reads to the first data storage system but not the second data storage system; and

servicing, by the first data storage system, the sequence of subsequent reads using prefetched data stored in the first data cache.

10. A non-transitory computer readable medium comprising code stored thereon that, when executed, performs a method of processing I/O operations comprising:

receiving, at a storage appliance from a host, a plurality of read operations directed to a logical device having its data replicated on a plurality of data storage systems, wherein the storage appliance virtualizes storage resources of the plurality of data storage systems by presenting the storage resources to the host as a single pool of storage;

sending, by the storage appliance, the plurality of read operations to a first of the plurality of data storage systems;

detecting, by the storage appliance, that the plurality of read operations form a sequential read pattern of consecutive reads directed to consecutive logical addresses of the logical device;

identifying, by the storage appliance, a plurality of next sequential logical addresses of the sequential read pattern of the logical device;

receiving, at the storage appliance from the host, a sequence of subsequent reads directed to the next sequential logical addresses of the sequential read pattern of the logical device;

determining, in accordance with one or more criteria, a set of the plurality of data storage systems that are candidates to perform processing for the sequence of subsequent reads, wherein the one or more criteria include information describing current configuration options of the plurality of data storage systems affecting I/O operation performance, said one or more criteria including, for each of the plurality of data storage systems for which the storage appliance virtualizes storage resources, an indication regarding whether said each data storage system performs sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the set includes the first data storage system and a second of the plurality of data storage systems, and wherein the criteria indicates that both the first data storage system and the second data storage system for which the storage appliance virtualizes storage resources perform sequential read pattern detection and data prefetching for detected sequential read patterns, wherein the first data storage system includes a first data cache used by the first data storage system and not used by the second data storage system, the second data storage system includes a second data cache used by the second data storage system and not used by the first data storage system, a first copy of the logical device is stored on physical devices of the first data storage system, and a second copy of the logical device is stored on physical devices of the second data storage system;

determining that the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system;

responsive to determining the plurality of read operations were previously sent to the first data storage system and not sent to the second data storage system, sending, by the storage appliance, the sequence of subsequent reads to the first data storage system but not the second data storage system; and

servicing, by the first data storage system, the sequence of subsequent reads using prefetched data stored in the first data cache.

11. The non-transitory computer readable medium of claim 10 , wherein the one or more criteria include an indication regarding whether each of the plurality of data storage systems performs data storage optimizations.

12. The non-transitory computer readable medium of claim 11 , wherein each data storage system in the set includes a plurality of storage tiers, each of the plurality of storage tiers having physical storage devices with performance characteristics that differ from other performance characteristics of other physical storage devices of other ones of the plurality of storage tiers, and wherein the data storage optimizations include automatically relocating data portions among the plurality of storage tiers in accordance with an I/O workload associated with each of the data portions.

13. The method of claim 1 , wherein the one or more criteria include, for each of the plurality of data storage systems, a data caching characteristic denoting a data cache eviction technique utilized by a data cache of said each data storage system, and a value denoting an amount of time a cached data item is expected to remain in a data cache of said each data storage system unless subsequently referenced during the amount of time.

14. The method of claim 1 , wherein the method includes:

performing processing on the first data storage system to recognize the sequential read pattern of the logical device and, prior to processing the sequence of subsequent reads, prefetch data of the next sequential logical addresses of the sequential read pattern of the logical device.