Dell PowerVault MD3600f/MD3620f Remote Replication Functional Guide

RR Suspend and Resume with Delta Log Resynchronization

It is important to be able to size the communications link for throughput and for IOPs. Peak period measurement for the application’s set of virtual disks is necessary in order to determine the bandwidth required for remote replication. Peak period IOPs measured will determine whether the intended distance of the remote site can support the peak IOPs. Additional factors that impact the peak period requirements include future growth needs, the need to share a single communications link, and whether there is a need to use redundant communications links for safety.

In the event that peak period write traffic exceeds the throughput and/or the IOPs capability of the communications links, it will be necessary to consider using RR’s Suspend and Resume features.

RRprovides the ability to suspend replication by explicitly using the Suspend command and under certain circumstances, to automatically suspend replication (consistency group suspension, asynchronous replication when link bandwidth exceeded). This allows RR to continue to capture all write I/Os but not use the overloaded communications links until a later time when the peak period traffic eases.

Asynchronous replication will automatically suspend when the peak period traffic exceeds the communications link capability (after exceeding the RR asynchronous queue).

AWOC will not automatically suspend when the peak period traffic exceeds the communications link capability. Instead host I/O will be slowed down to keep the peak period traffic below the link capability. This preserves data integrity of the remote virtual disks without resorting to RR suspension.

Suspending replication will create a delta log for each affected virtual disk at the time of suspension. This delta log tracks the missing write I/O to the remote virtual disk for the duration of the suspension and marks a data range for the write and will use this delta to sequence writes to that remote virtual disk when RR resumes.

Resume will cause RR to resume replication for the suspended virtual disk. The delta log will be read front to back from the primary virtual disk for all the missing I/Os in the secondary virtual disk and RR will send these missing I/Os to the secondary MD36X0f. Once the delta log is completely processed, RR resumes active replication of the primary virtual disk.

It is important to note that the delta log reads will be larger than the original write I/O due to the fact that the delta log is composed of data ranges that are often larger than I/Os. Because the delta log is fixed in size, larger virtual disks will have larger data ranges. This means the resumption time may be longer than it would have taken if RR did not suspend.

If the communications link is sufficiently undersized (for example, due to peak period traffic growth), there is the possibility that the RR resume operation may never complete. The assumption for the resume operation completing is that there is sufficient time and bandwidth to process all missing writes in the delta log before the next peak period occurs. This may not be the case if the peak period traffic continues or if the non-peak traffic prevents emptying the delta log.

It is important to size the communications link to handle current workloads, future growth, and RR resume operations.

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Dell MD3620F, MD3600f manual RR Suspend and Resume with Delta Log Resynchronization
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MD3620F, MD3600f specifications

Dell's MD3620F and MD3600F storage arrays are designed for businesses seeking dependable, high-performance storage solutions tailored to meet the demands of modern data management. These models offer a blend of scalability, efficiency, and advanced features, making them well-suited for a range of applications, from virtual environments to critical database operations.

One of the primary features of the MD3620F and MD3600F is their support for a hybrid storage architecture. This approach allows organizations to combine flash storage with traditional hard disk drives (HDDs) to optimize performance and cost. The MD3620F focuses heavily on all-flash configurations, delivering exceptional speed and lower latency, ideal for I/O-intensive workloads.

Scalability is another hallmark of these storage solutions. The MD3600F allows users to scale up to 120 drives, providing robust capacity to meet growing data needs. The MD3620F is engineered for environments where data availability and speed are paramount, with support for high IOPS (Input/Output Operations Per Second) and consistent performance under stress.

In terms of data management, both systems integrate with Dell’s proprietary software, which enhances operational efficiency through features like automated tiering. This technology optimizes data placement between different storage types based on access frequency, ensuring that hot data is readily available while reducing costs associated with less critical data.

Reliability is crucial for businesses that depend on their storage systems. The MD3620F and MD3600F come equipped with advanced data protection mechanisms, such as RAID support, which safeguards against data loss, and snapshot capabilities that provide point-in-time copies of data. Moreover, these solutions include hot-swappable components, ensuring minimal downtime for maintenance and repairs.

Connectivity is also a strong suit of these storage arrays. They support multiple connectivity options, including SAS and iSCSI, allowing for flexible integration into existing IT infrastructures. This adaptability enhances their appeal to a wide range of enterprise environments.

In summary, the Dell MD3620F and MD3600F stand out as robust storage solutions with a combination of hybrid and all-flash configurations, scalability, advanced data management tools, and enhanced reliability features. These characteristics make them ideal for organizations looking to enhance their data storage capabilities while maintaining high performance and efficiency.
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