On Fri, September 8, 2017 3:06 pm, John R Pierce wrote:
> On 9/8/2017 12:52 PM, Valeri Galtsev wrote:
>> Thanks. That seems to clear fog a little bit. I still would like to hear
>> manufacturers/models here. My choices would be: Areca or LSI (bought out
>> by Intel, so former LSI chipset and microcode/firmware) and as SSD
>> Samsung
>> Evo SATA III. Does anyone who used these in hardware RAID can offer any
>> bad experience description?
>
>
> Does the Samsung EVO have supercaps and write-back buffer protection?Â
> if not, it is in NO way suitable for reliable use in a raid/server
> environment.
With all due respect, John, this is the same as hard drive cache is not
backed up power wise for a case of power loss. And hard drives all lie
about write operation completed before data actually are on the platters.
So we can claim the same: hard drives are not suitable for RAID. I implied
to find out from experts in what respect they claim SSDs are unsuitable
for hardware RAID as opposed to mechanical hard drives.
Am I missing something?
>
> as far as raiding SSDs go, the ONLY raid I'd use with them is raid1
> mirroring (or if more than 2, raid10 striped mirrors). And I'd probably
> do it with OS based software raid, as thats more likely to support SSD
> trim than a hardware raid card, plus allows the host to monitor the SSDs
> via SMART, which a hardware raid card probably hides.
Good, thanks. My 3ware RAIDs through their 3dm daemon do warn me about
SMART status: fail (meaning the drive though working should according to
SMART be replaced ASAP). Not certain off hand about LSI ones (one should
be able to query them through command line client utility).
>
> I'd also make sure I undercommit the size of the SSD, so if its a 500GB
> SSD, I'd make absolutely sure to never have more than 300-350GB of data
> on it.  if its part of a stripe set, the only way to ensure this is to
> partition it so the raid slice is only 300-350GB.
Great point! And one may want to adjust stripe size to be resembling SSDs
internals, as default is for hard drives, right?
Thanks, John, that was instructive!
Valeri
>
>
> --
> john r pierce, recycling bits in santa cruz
>
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++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++
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