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Samsung Enterprise SSD Drives - RAID controllers with TRIM support

Posted on 2016-10-31
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Last Modified: 2016-12-21
I was looking at some Samsung Enterprise SSD Drives (PM863) and had a question about garbage collection. I couldn't find the answer on their web site so I called. They said there was no voice contact (support) on these drives and if you can't find the answer on our web site there isn't anything you can do. If that is true, that these drives have no support, why would anyone buy them? Does anyone know if that is true that they have not support? Does anyone know if they do garbage collection?

   Along that same line.... I chatted with Intel about their Datacenter SSD drives and their knowledge was less than stellar. They said there are RAID controllers out now that support TRIM but couldn't give me any manufacturers or model numbers. Does anyone know of any?
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Question by:LockDown32
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by:andyalder
ID: 41867351
You don't need TRIM with PM863 because there's enough over-provisioning for efficient background garbage collection from what I've read, for example the 960GB is actually 1TiB internally. However I can't find the article I read it in and can't find anything on Samsung's website either except for the endurance figures in the drive's specsheet.

As far as RAID controllers that support TRIM I think Intel are wrong there, there are RAID controllers that support TRIM in pass-through mode but then it's not really a RAID controller if it's working in HBA mode.
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by:LockDown32
ID: 41867377
That is what scares me. You would think that if it didn't need TRIM for what ever reason that it would be a major selling point and should be on their web site. I believe I read the same article but it would sure be nice to see that statement on their web site.

    and the fact that there is no one in support to ask actually blows my mind. What kind of operation is that? I for one can't buy something that has no support and this is one prime example of why. What were they thinking......
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by:andyalder
ID: 41867414
It may have been http://www.samsung.com/us/system/b2b/resource/2015/03/16/WHP-SSD-DATACENTER-FEB15J.pdf but it really only mentions that the advanced flash controllers in enterprise SSDs are designed to reduce write amplification to near 1 without saying how they use the extra space and the onboard RAM plus capcitors to achieve it.
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by:LockDown32
ID: 41867430
They mention garbage collection twice in the article but never say their drives to it. Very, very odd. If I had to guess those drives don't do any garbage collection. What a shame.....
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by:andyalder
ID: 41867547
Garbage collection is bad as it leads to write amplification, the enterprise SSD minimises it by using the overprovisioned space but I'm certain they do do it if they have to, otherwise the SSD would run out of space when it was only 10% full. You'll note that the article also only mentions overprovisioning as something users do with workstation SSDs but of course the enterprise SSD's  overprovisioning (and GC) is hidden from view behind the advanced flash controller which they won't tell us anything about except to say it's wonderful.
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by:LockDown32
ID: 41867562
Garbage collection is bad? All the articles I have read very plainly state that if no garbage collection is done that the life of the SSD gets drastically reduced and writes, over time, will take much, much longer.  One of the big plus's Intel has going for their Datacenter drives is background garbage collection. You can put them on a RAID controller and they do their on garbage collection. TRIM is not needed. One way to help is over provisioning. Samsung might do both but they sure don't mention it if they do. Either they don't do either or they need to fire their marketing department :)
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by:andyalder
ID: 41867655
Of course GC is bad, let's assume we have a tiny SSD which has 4 blocks and each block is composed of 4 x 4K pages. the OS writes in 4K sectors and for this simulation will write to each 4K sector four times. V=valid data, S=stale data, 0=clean

sectors written      Aggressive GC                                                        Lazy GC

0                                   0000 0000 0000 0000                                 0000 0000 0000 0000
4                                    sssv 0000 0000 0000                                 sssv 0000 0000 0000
8                                    sssv sssv 0000 0000                                   sssv sssv 0000 0000
aggressive cleans, lazy doesn't
8                                   0000 0000 vv00 0000                                  sssv sssv 0000 0000
12                                 0000 0000 vvss sv00                                   sssv sssv sssv 0000
both clean
12                                 vvv0 0000 0000 0000                                  0000 0000 0000 vvv0


After just 12 writes using my none-too-clever OS write pattern the aggressive GC algorithm has cleaned one more block than the lazy algorithm has and it is this cleaning of blocks that wears SSDs out. GC is a harmful but necessary process.
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by:LockDown32
ID: 41868154
You hit it with your last comment. What it does is bad but not doing it is worse. Guess it depends on how you look at it.
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andyalder earned 500 total points
ID: 41868279
Not doing garbage collection at all makes it into a WORM device as blocks would never get cleaned.

I guess Samsung's sales support have the same problem I have, there's meant to be a whole bunch of PDFs under the data center tab of http://www.samsung.com/global/business/semiconductor/minisite/SSD/M2M/html/whitepaper/whitepaper09.html but none of them open.
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