Raid controller

Created: Nov 30, 2019 04:00:48Latest reply: Nov 30, 2019 06:24:47 84 2 1 0
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Hi,

What's the purpose of Cache on Raid controller? And how does it effect the overall performance.
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stephen.xu
Admin Created Nov 30, 2019 04:40:31 Helpful(3) Helpful(3)

Hello, umaryaqub


The purpose of the RAID controller cache is to improve the data read/write performance, 


Read Ahead: The controller card caches the data that follows the data being read for faster access. This policy reduces drive seeks and shortens read time.


Write Back: After the cache receives host data, the controller card signals the host that the data transmission is complete.

Data is directly written to the cache. The controller card then updates accumulated cache data to hard drives in batches. Overall data write speed is higher since writing to the cache is faster than writing to the hard drive.


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stephen.xu
stephen.xu Admin Created Nov 30, 2019 04:40:31 Helpful(3) Helpful(3)

Hello, umaryaqub


The purpose of the RAID controller cache is to improve the data read/write performance, 


Read Ahead: The controller card caches the data that follows the data being read for faster access. This policy reduces drive seeks and shortens read time.


Write Back: After the cache receives host data, the controller card signals the host that the data transmission is complete.

Data is directly written to the cache. The controller card then updates accumulated cache data to hard drives in batches. Overall data write speed is higher since writing to the cache is faster than writing to the hard drive.


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  • convention:

wissal
wissal MVE Created Nov 30, 2019 06:24:47 Helpful(2) Helpful(2)

Hello,

The purpose of RAM on a RAID controller is to provide a level of cache to allow write operations to hit stable storage without incurring the latencies involved with rotating disks.

The RAM on the controller can usually be split between read and write cache. A common ratio is 75:25 write:read.

Write caching is helpful because applications can write to low-latency controller memory with no delay. That data then gets flushed to disks, which are an order of magnitude slower.

Read caching helps keep hot or frequently-used data on the controller's memory so that requests don't need to be fetched from slower disks.

The memory is used for read and write cache which improves the performance of the storage. The basic rule when it comes to cache is buy as much as you can afford. The more cache you have the better the performance of the disks will be as data can be written to the memory if the disks aren't in the correct position.

You'll also need to make sure that the RAID card has a battery built on to protect the data in the write cache if there is a power outage.

Thanks

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