LSI Fastpath and cache memory

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Jesin A

New Member
Oct 6, 2015
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I was looking at Fastpath's benchmarks from the LSI product brief and the following were the Virtual drive settings for the tests:

Write policy: Write Through
I/O policy: Direct IO
Read policy: No Read Ahead
Disk Cache: Enabled

Looking at the MegaRAID user guide it seems these settings pass requests to the SSDs directly, bypassing the cache memory on the card. Is my understanding correct?

Does that mean a BBU or Cachevault isn't needed if using Fastpath as nothing is stored to the cache memory?
 

TuxDude

Well-Known Member
Sep 17, 2011
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With any RAID controller, if the write cache (write policy, whatever...) is set to Write Through there is no need to have a BBU - write-through mode does not cache writes.

It may or may not still be caching reads, but no need for a BBU for that.
 

Jesin A

New Member
Oct 6, 2015
8
1
3
Thanks for the quick response @TuxDude.

That brings me to the next question. If FastPath doesn't use the cache, how is it different from software RAID with SSDs?

Hardware RAID will definitely be better when parity calculations are involved but for RAID 0,1 and 10 software RAID does the same for writes. Does that make the performance of RAID 10 on FastPath equivalent to software RAID?