SSD L2 Writeback Cache Question

[DarkDiamond]

Hi,

I am considering building out a raid array based on slower WD Red NAS drives and have a question about using SSD's as a write back cache. Would mirroring a pair of SSDs with on board capacitors and using that mirror as a L2 write back cache be enough of protection to prevent data loss in the event of a power failure? Basically all writes would go to the SSD cache first and then be written out to the hard drives. I was thinking this configuration could blunt the reduction of IOPS as a result of using slower larger spinning SATA drives? Is there anything else I should consider? Is this a really bad idea?

Thanks!
Chris

[Max (staff)]

Hi!
I'm not sure that's a necessary measure.
In case of a power outage you're still dealing with application failures caused by sudden blackout.
So adding an extra layer of protection to just storage doesn't justify itself.

As for the IOPS, using SSD for write-back doesn't eliminate the bottleneck of the disks themselves.
You have to understand that the moment the cache fills up you'll get a performance drop down to the SATA speeds.
Although, this idea might be good if you keep an oversized SSD cache.