what is fst

Fast failover is a new feature that improves the failover time for the storage stack configured in a clustered environment. Fast failover includes several design changes and enhancements to the core SFW components. These changes provide significant reduction in the failover time taken by storage resources during service group failovers.

The following factors determine how fast SFW fails over the storage stack:

How fast the clustering software detects a fault

How fast SFW is able to get the fault notification

Storage management and remedial actions

How SFW manages configuration changes and the actions it takes on the storage

With fast failover, SFW addresses Fault notification and Storage management and remedial actions factors. SFW has optimized the algorithms and enhanced the internal logic used to manage disk groups and the storage configuration changes across the nodes in a cluster.

Cluster Server (VCS) addresses the Fault detection factor with the Intelligent Monitoring Framework (IMF) feature that provides instantaneous fault detection capability.

Fast failover integrates with the IMF feature to provide a significant performance improvement in SFW HA cluster environments.


what is fst

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How is disk speed measured and what is fast? How long should a copy of 1500 GB take?

How is disk speed measured? Is it Mbit or Mbyte per second read? What is average today and what is fast and what is very fast in the industry?

Let's say somebody says it takes a long time to make a copy of a file of 1500 GB (say a database file), how long would that take on a professional system and how can that be calculated taking the speed of the hard disk into acount?

Disk speeds are usually measured in;

  • Rotational speed in revolutions per minute (lowest at 4200rpm, then 5400, 7200, 10k and 15k - this isn't applicable to SSDs or flash memory).
  • Interface speed is the fastest a disks electronics can try to send the data to the disk controller (these range from ATA's 100MBps through SATA's 150/300/600 Mbps, Fibre-Channel's 2/4/8/16 Gbps and even to PCIe speeds for flash-based storage such as FusionIO).
  • Seek time is simply the time it takes to start reading or writing a particular sector of disk - these can range from 3-15ms for disks to a small fraction of this for SSD/flash disks.
  • Then we get to actual speed you can expect, there are four speeds you should care about; sequential read (reading a very large block of data), sequential write (same but writing), random read (getting data from all over the disk) and random write. These vary enormously but for spinning disks you can expect anything from 25MBps-to-150MBps for sequential read and write and anything from 3MBps-to-50Mps for random read and write. SSDs are typically in the 200MBps range for sequential and usually a little less for random operations. FusionIO can easily hit 1GBps for all, but are typically small and expensive.

As you can see there is no real average, if you'd like recommendations on what to buy please feel free to come back to us with as much information as you can - this should include budget, application type, data set size, user base, hardware/OS plus anything else you think would be useful.

As for your 1.5TB copy, well if you were doing this to a USB 2-attached 7200rpm SATA disk you should get at least 30MBps-40MBps or so the full 1.5TB could take over 10 hours or so. If this were a typical professional DAS/SAN system I'd expect in the region of 100MBps meaning it'd take around 3 hours.

Hope this helps, oh and just to clarify, MB=megabytes, Mb is megabits.


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