On 07/02/2015 07:01 AM, Wes Vaske (wvaske) wrote:
What about a RAID controller? Are RAID controllers even available for
PCI-Express SSD drives, or do we have to stick with SATA if we need a
battery-backed RAID controller? Or is software RAID sufficient for SSD
drives?
Quite a few of the benefits of using a hardware RAID controller are
irrelevant when using modern SSDs. The great random write performance
of the drives means the cache on the controller is less useful and the
drives you’re considering (Intel’s enterprise grade) will have full
power protection for inflight data.
For what it's worth, in my most recent iteration I decided to go with
the Intel Enterprise NVMe drives and no RAID. My reasoning was thus:
1. Modern SSDs are so fast that even if you had an infinitely fast RAID
card you would still be severely constrained by the limits of SAS/SATA.
To get the full speed advantages you have to connect directly into the bus.
2. We don't typically have redundant electronic components in our
servers. Sure, we have dual power supplies and dual NICs (though
generally to handle external failures) and ECC-RAM but no hot-backup CPU
or redundant RAM banks and...no backup RAID card. Intel Enterprise SSD
already have power-fail protection so I don't need a RAID card to give
me BBU. Given the MTBF of good enterprise SSD I'm left to wonder if
placing a RAID card in front merely adds a new point of failure and
scheduled-downtime-inducing hands-on maintenance (I'm looking at you,
RAID backup battery).
3. I'm streaming to an entire redundant server and doing regular backups
anyway so I'm covered for availability and recovery should the SSD (or
anything else in the server) fail.
BTW, here's an article worth reading:
https://blog.algolia.com/when-solid-state-drives-are-not-that-solid/
Cheers,
Steve
