I want to bring the discussion about “VNX data replication” to your attention. It’s on ECN and the URL is https://community.emc.com/thread/149825. If you want to ask about replication specifically, you can post your questions here or on ECN.
The author, Rupal Rajwar is USPEED certified and works for EMC eServices Customer Support division since 2010.
Although the actual story I want to point out to you is on the EMC Community Network website (also called ECN), I would like to invite you to join the discussion there:
https://community.emc.com/thread/148025?tstart=0
If you’d like to discuss anything here, you’re welcome to do so.
Let’s join the discussion!
How does an EMC Clariion or VNX decide which Hot Spare will be used for any failed drive?
First of all not the entire failed drive will be rebuilt, but only the LUNs that reside on the failed drive. Furthermore all LUNs on the failed drive will be rebuilt to the same Hot Spare, so a single failed drive will be replaced by a single Hot Spare. So if for example a 600GB drive fails with only 100GB worth of LUNs on it, in theory a 146GB drive could be invoked to rebuild the data. The location of the last LUN block on the failed drive specifies how large the Hot Spare needs to be. If on a 600GB drive the last block of the last LUN sits on “location 350GB”, but the amount of disk space used by all LUNs residing on that drive is 100GB, the 146 and 300GB Hot Spares aren’t valid choices, since the last block address is beyond the 300GB mark (350GB). So valid Hot Spares would be 400GB or larger.
It’s out there since quite a few years already. It started becoming available to the general public about 12 years ago or so and was commonly seen in digital cameras: FLASH storage! At first the devices couldn’t store more than just a few MB and prices were high, but over time the size went up and prices went down and the first SSD drives (should we say “drives”?) were born. Still expensive but they were very usable in the computer industry. Mainly heavily used databases could be accelerated by using SSD because there was no rotational latency and avg access latency was in the sub mili second range instead of multiple mili seconds! The common problem in the last few years was mainly durability, but currently the SSD technology is just as reliable as the old rotating disks.
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