Flash-backed RAID cards - consumer level?

H

HaxNobody

n00b
Joined
Nov 20, 2012
Messages
53
Hey guys, I recently suffered a failure on my SSD RAID 0 that likely wouldn't have been as bad if I would have had a RAID card with some kind of BBU. Currently, I'm just running off my consumer level ASUS mobo and I had write-back caching enabled and buffer flushing turned off. My bad.

What I want to know is this - are there any "consumer level' RAID cards that have flash-backed caches instead of battery backed caches (use a super capacitor)? I'm running Sammy 840 pros right now, as well as a pair of spinners in RAID 1 for backup storage.

If there's nothing that's really available as "consumer level", what would be the best enterprise alternative that won't break the bank? And would it be compatible with my existing drives (TLER considerations and all that....)?

Until I figure something out, I have write-through caching set up and buffer flushing turned on to prevent issues again. BTW, I do have a UPS on this machine, but for some strange reason the mobo decided that it was getting dirty power and just shut down for no reason, which caused issues for whatever may have been in the cache at that time.
 
Buffer flushing should always be turned on, even with a battery/flash backed RAID card. The point is that only with a flush it can only be guaranteed that the writes actually arrived completely in the RAID cards RAM cache. The difference beween writeback and writethrough is, that in writeback the card returns from buffer flushes much faster.

In my opinion it makes no sense to use a RAID card flash backed cache with 840 Pros. The 840 Pro has no power-loss protection. The card flushes the writes to the SSD, at which point the data is safe from the point of view of the card. But an SSD without PLP may still lose the data.

Finally, there is no really cheap solution to your problem. I got a used 9271-4i card for 150€ a while ago. A CacheVault module would cost around ~100€. But for the data to be safe I would have to get SSDs with PLP like the Intel S3500.

But in basically no case you should turn off buffer flushing. A UPS would reduce the risk, but a system crash can still screw up your data. My personal suggestion would be to forget about RAID0 and use a single 840 Pro, probably with RAPID if that makes sense for your workload. Or invest in a PCIe SSD, this would still be cheaper that a new RAID card.
 
Last edited:
I figured that I couldn't really go wrong with just about any LSI card, and CacheVault would be the answer. I'll have to see if i can find something at a good price. Interesting point about the SSDs, I didn't even know that that was a consideration. Are there any other (cheaper) options that would have some form of PLP?

I guess I shouldn't complain though, because even the S3500s are less than $1/gb brand new, which is a testament to how fast flash prices have been coming down. The main issue is that I'm trying to stick to a really small form factor, and unfortunately the small motherboards only ever have one PCI-E slot especially if I use a double-wide graphics card.

Until now, I have been seriously loving my dual SSD RAID 0 performance for my OS drive, but I should have expected this to happen sooner or later. Maybe I'll just have to build something bigger.
 
HaxNobody said:
Interesting point about the SSDs, I didn't even know that that was a consideration. Are there any other (cheaper) options that would have some form of PLP?
Click to expand...

Crucial M550

Some of the enterprise-oriented Samsung drives have the capacitors. Not sure offhand which ones, but I think one of the ones that has them is the SM843T.
 
The Crucial non-enterprise drives do not have full PLP. They have enough capacitors to not corrupt their mapping table, and thus the data already on flash. Those measly ceramic caps are not enough to write their DRAM cache to NAND.

This should be evident if you look at the M500DC (datacenter). Those have an array of tantalum caps like the Samsung 845DC, the Intel 320 and Seagate Pro 600. And, like the other vendors charge you extra for this. They also have some nice performance characteristics compared to the consumer drives (i.e. much shorter write latencies).

If you absolutely cannot live without the added performance over a single SSD I suggest to wait till the Intel P3500 PCIe SSD is available. These will blow any RAID0 of SATA SSDs out of the water and comes with PLP. The RAID controller is will basically only boost writes, while the PCIe SSD improves read performance by an order of magnitude at least.
 
Last edited:
Good point about the PCIe option. I guess a bigger build would be in order anyways, since I have only one slot now. I like having a tiny box of power that blows all the big stuff out of the water. However the PCIe option is top-tier, and Intel sure likes to show that off with their pricing. I can buy 2 new 480gb S3500s, the aforementioned 9271-4i, a CacheVault kit, and a FastPath license key for less than the PCIe SSD by itself.
 
NVM I see you said P3500 which has not been released yet; I was looking at the P3600. Any pricing/availability dates for the P3500?
 
There are price estimations of 500-600$ for the 400 GB version.
Sadly, there is no release date, it seems that Intel is trying to squeeze a bit more out of the P3600 sales before they bring the P3500 to the market.
The S3700 was released earlier than the S3500, too, even though the controller is the same and the flash should have been better available.

The RAID controller solution might be cheaper, but the PCIe SSD will easily destroy it for any type of read workload.
 
I'll definitely keep it in mind for my next build which will hopefully be a few years down the road. For now, I have disabled "Anti-Surge Protection" in the BIOS of my Maximus VI Impact, enabled buffer flushing, and switched from Write-back to Write-through. Hopefully this will prevent any more sudden power loss and corruption.
 
You must log in or register to reply here.
Back
Top