Radian RMS-200 $99/OBO

tonkyhonk

New Member
Feb 3, 2021
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This reminds me of the PCIe AIC thing where it took a regular stick of DDR3 RAM and made it accessible
Kinda like a RAMdisk
but in hardware
 
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EasyRhino

Active Member
Aug 6, 2019
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So it's.... 8GB of DRAM backed by 8GB of flash in the event of power failure?

What would the use case of this be? is 8GB really enough for a SLOG?
 

Stephan

Active Member
Apr 21, 2017
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8 GB is plenty up to around 10 Gbit/s connections of servers. With default zfs_txg_timeout of 5 seconds there is worst-case space for 8 GB / 5 seconds / 3 in-flight txg groups ~= 0,5 GB /sec of _sync_ writes. Good enough for I'd say 8-12 HDD RAIDZ2 configurations. For SSD pools I'd use Optane because it reduces writes to the pool, i.e. prolongs SSD life. See SLOG Devices |
 
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lowfat

Active Member
Nov 25, 2016
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How is this better than just using 16 gb of ramdisk as slog?
Using a ramdisk for an SLOG is useless. SLOG = second intent log. There is already an intent log being written to ram. An SLOG is just a backup in case of power loss. But enabling it slows the LOG to the speed of the SLOG. With the above solution you get near DRAM level of performance for an SLOG, yet still have power loss protection.
 

Markess

Well-Known Member
May 19, 2018
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Using a ramdisk for an SLOG is useless. SLOG = second intent log. There is already an intent log being written to ram. An SLOG is just a backup in case of power loss. But enabling it slows the LOG to the speed of the SLOG. With the above solution you get near DRAM level of performance for an SLOG, yet still have power loss protection.
This is a really nice, clear, concise explanation. A while back, I tried to explain this to my son and I didn't do a great job: I think I left him more confused after than he was before!
 

tinfoil3d

QSFP28
May 11, 2020
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I just absolutely dont get who would want this instead of RAM. Redundancy? Put the data to two severs simultaneously. Put it to nvme. Those classic mlc/slc nvmes are only few times slower than RAM.
 

NablaSquaredG

Active Member
Aug 17, 2020
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I just absolutely dont get who would want this instead of RAM.
Everyone who understood that normal RAM is a really bad idea, because Machine failure / Power failure will lead to data loss.

Redundancy? Put the data to two severs simultaneously.
ZFS is (typically) not a Distributed filesystem. ZFS is not Ceph. And even if it worked with ZFS, you're still gonna have a bad day in case of a power failure without UPS (both servers failing at the same time)
Adding another server also introduces the requirement for a quorum, which adds a lot of complexity.
Plus you double the power consumption by adding a second server...

Put it to nvme. Those classic mlc/slc nvmes are only few times slower than RAM.
"only a few times"... Dude, are you even trying?

The difference in IOPS between RAM and SSDs is MASSIVE.

There's a good reason why the only SSD (sensible) people use as SLOG are Intel Optane SSDs (like the 900p). With almost every other SSD as SLOG, your storage is gonna be dead slow.

What you want as SLOG is basically
1. NVDIMM-N (e.g. Micron NVDIMM-N, Radian RMS 200, etc...)
2. NVDIMM-P (e.g. Intel Optane DCPMM)
3. Optane SSDs (e.g. 900p)

(ordered after decreasing performance. Normal SSDs include because that's a terrible idea)
 
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NablaSquaredG

Active Member
Aug 17, 2020
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The Radian 200 isn't an SSD, is it?
It's basically an PCIe attached NVDIMM-N, with the 200 generation based on DDR3 and the 300 generation based on DDR4
 

NablaSquaredG

Active Member
Aug 17, 2020
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You were saying "Radian SSD"

The Radian stuff only uses the flash in case of power failure. So it's essentially a NVDIMM-N
 

poots

New Member
Jul 12, 2018
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This shows up as a 8gb NVMe block device, in case anyone was wondering. Worked during testing on a HP Z820 workstation running Windows 10 Pro, and in a Dell R720XD running Debian 10.

It uses DDR3 RAM as the main storage, which is backed by a supercap and a flash chip. When you power it on, it reads off the flash chip and dumps it into RAM. When you power it off, it dumps it back into flash. That's what makes it "Non-Volatile"
 
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