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? 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 ++++++++++++++++++++++++++++++++++++++++