On 04/04/2014 10:15 AM, Merlin Moncure wrote:
2. Do I need both BBU on the RAID *and* capacitor on the SSD or just on one?
Which one? I'm suspecting capacitor on the SSD and write-through on the
RAID.
You need both. The capacitor protects the drive, the BBU protects the
raid controller.
?? In write-through the controller shouldn't return success until it
gets it from the drive so no BBU should be required. One LSI slide deck
recommends write-back as the optimum policy for SSDs. But I could be
wrong which is why I ask.
2. Current thoughts on hardware vs. software RAID - especially since many of
the current SSD solutions plug straight into the bus.
IMNSHO, software raid is a better bet. The advantages are compelling:
Cost, TRIM support, etc. and the SSD drives do not benefit as much
from the write cache. But hardware controllers offer very fast burst
write performance which is nice.
6. Thoughts on "best bang for the buck?" For example, am I better off
dropping the RAID cards and additional drives and instead adding another
standby server?
This is going to depend a lot on write patterns. If you don't do much
writing, you can gear up accordingly. For all around performance, the
S3700 (2.5$/gb) IMO held the crown for most of 2013 and I think is
still the one to buy. The s3500 (1.25$/gb) came out and also looks
like a pretty good deal, and there are some decent competitors (600
pro for example). If you're willing to spend more, there are a lot of
other options. I don't think it's reasonable to spend less for a
write heavy application.
FWIW, the workload is somewhat over 50% writes and currently peaks at
~1,600 queries/second after excluding "set" statements. This is
currently spread across four 15k SATA drives in RAID 10.
Judicious archiving allows us to keep our total OS+data storage
requirements under 100GB. Usually. So we should be able to easily stay
in the $500/drive price range (200GB S3700) and still have plenty of
headroom for wear-leveling.
One option I'm considering is no RAID at all but spend the savings from
the controllers and extra drives toward an additional standby server.
Cheers,
Steve
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