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SSD in a RAID 0 - How effective is Background Garbage Collection

post #1 of 11
Thread Starter 
So, If I put 3 SSD's with BGC (Background Garbage Collection) in a RAID 0, how effective is BGC or does it even work when in a RAID 0?

Does anyone even notice performance differences after heavy use then left idle?

Thanks
Edited by Dookie_Brown - 1/29/11 at 1:39pm
post #2 of 11
Thread Starter 
Bump....... :oP
post #3 of 11
Quote:
Originally Posted by Dookie_Brown;12096200 
So, If I put 3 SSD's with BGC (Background Garbage Collection) in a RAID 0, how effective is BGC or does it even work when in a RAID 0?

Does anyone even notice performance differences after heavy use then left idle?

Thanks

Depends on the SSD. Sandforce drives are supposed to have great BGC, Crucial drives are a close second, and Intel drives have none. Yes, unlike TRIM, BGC is active when the drives are in RAID.

It's very doubtful you'll feel feel a big performance difference unless you swamp your drive with incompressible data, delete it, and then leave it on idle for a couple of days.

Edit: Fill in your System Information here, it might help answer the question.
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post #4 of 11
Unless you're constantly moving tons of data every day I wouldn't worry about it. I got my C300's on raid 0 and I haven't noticed any loss in performance over the last couple months.
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post #5 of 11
Thread Starter 
Quote:
Originally Posted by thisischuck01;12189606 
unlike TRIM, BGC is active when the drives are in RAID.

This leads me to my next question. If TRIM works with the OS to wipe the data when deleting a file, how does BGC know that the RAID stripe or block used is actually part of a file if it is independent from the OS? Does BGC talk to the RAID controller so it knows that when I delete a 4GB .mkv file it will wipe those storage bits?

Honestly, I just don't see how BGC will work if all the block level data is handled by the RAID card and BGC is on the controller of the SSD.
post #6 of 11
Quote:
Originally Posted by Dookie_Brown;12290886 
This leads me to my next question. If TRIM works with the OS to wipe the data when deleting a file, how does BGC know that the RAID stripe or block used is actually part of a file if it is independent from the OS? Does BGC talk to the RAID controller so it knows that when I delete a 4GB .mkv file it will wipe those storage bits?

Honestly, I just don't see how BGC will work if all the block level data is handled by the RAID card and BGC is on the controller of the SSD.

TRIM is a function of the OS, while BGC is a function of the SSD controller. If you have two drives in RAID, each drive's controller will perform the BGC command. This action is done completely independent of any other drives (even if the drives are in RAID) and the OS. TRIM, on the other hand, will recognize the two drives as one (because the OS does not recognize the RAID array as more than one drive), and therefore won't be able to function correctly.

A RAID controller only deals with the processes of data (affects IO speeds) and drive setup. It doesn't deal with the data itself.

EDIT:
From Wikipedia:
Quote:
A disk array controller is a device which manages the physical disk drives and presents them to the computer as logical units.

Edited by thisischuck01 - 2/7/11 at 9:06am
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post #7 of 11
Thread Starter 
Quote:
Originally Posted by thisischuck01;12295729 
If you have two drives in RAID, each drive's controller will perform the BGC command. This action is done completely independent of any other drives (even if the drives are in RAID) and the OS.

Here's where i'm confused. If the BGC is independent of anything, how does BGC know that blocks ACEGI is part of a my 4GB .mkv file and is a portion of BDFHJ? To BGC those are just bits of data. How does BGC know NOT to wipe those bits because it is part of an actual file within a RAID 0 stripe of 16K or 32K or 64K or 128K from the RAID controller?

RAID 0
SSD0 SSD1
A
B
C
D
E
F
G
H
I
J

What flags BGC to wipe and not wipe?
If BGC does not talk to the RAID controller to determine if the RAID block size of 16K or 32K or 64K or 128K is being used and no data is actually being accidentally "wiped" by BGC, then is BGC even really working at all?

I understand that the RAID controller handles the LUN presentation to the OS but how does BGC interpolate what bit's in a RAID block is part of an actual file if all BGC sees is independent of itself, a data bit. So what flags BGC to wipe and not wipe if the blocks written to are RAID blocks and not OS blocks. Does the SSD's controller keep track of the data written and read to/from?

EDIT:
OK, the formatting of my blocks didn't come across, my bad.
Edited by Dookie_Brown - 2/7/11 at 10:16am
post #8 of 11
Here's a comparison between my C300 RAID almost 6 months ago to now.
I've done nothing special to my array, ran no special tools/software, just reagular day-to-day tasks.
The only change is an updated driver for the intel controller (thus the faster small file writes).

The write speeds are what you want to be looking at anyways, those are what will degrade the fastest with an SSD.

6 Months Ago:
191142d1295462510-faster-atto_ssd_raid0.png

Just now:
attachment.php?attachmentid=194495&stc=1&d=1297125099
Edited by Dark - 2/7/11 at 4:35pm
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post #9 of 11
Quote:
Originally Posted by Dookie_Brown;12296014 
Here's where i'm confused. If the BGC is independent of anything, how does BGC know that blocks ACEGI is part of a my 4GB .mkv file and is a portion of BDFHJ? To BGC those are just bits of data. How does BGC know NOT to wipe those bits because it is part of an actual file within a RAID 0 stripe of 16K or 32K or 64K or 128K from the RAID controller?

RAID 0
SSD0 SSD1
A
B
C
D
E
F
G
H
I
J

What flags BGC to wipe and not wipe?
If BGC does not talk to the RAID controller to determine if the RAID block size of 16K or 32K or 64K or 128K is being used and no data is actually being accidentally "wiped" by BGC, then is BGC even really working at all?

I understand that the RAID controller handles the LUN presentation to the OS but how does BGC interpolate what bit's in a RAID block is part of an actual file if all BGC sees is independent of itself, a data bit. So what flags BGC to wipe and not wipe if the blocks written to are RAID blocks and not OS blocks. Does the SSD's controller keep track of the data written and read to/from?

EDIT:
OK, the formatting of my blocks didn't come across, my bad.

It compares the data on the drive to the Master File Table, when a file is deleted the record in the MFT is removed but the data usually remains (think of a windows 'quick' format to a 'full' format, a quick format merely wipes the table when a full format writes over the entire disc). Garbage Collection compares the two and removes the ones with no association.
I'm almost certain it executes other forms of GC as well.
Edited by Dark - 2/7/11 at 4:45pm
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post #10 of 11
Thread Starter 
Quote:
Originally Posted by Dark;12301360 
It compares the data on the drive to the Master File Table, when a file is deleted the record in the MFT is removed but the data usually remains (think of a windows 'quick' format to a 'full' format, a quick format merely wipes the table when a full format writes over the entire disc). Garbage Collection compares the two and removes the ones with no association.
I'm almost certain it executes other forms of GC as well.

Am I reading you correctly if I say that "the on board controllers of each SSD DOES IN FACT talk to the RAID controller card to read the MFT of the presented RAID disk LUN? in order for BGC to 'Know' which blocks of data to wipe?"

This is contradictory to what some say but it does make perfectly good sense.

Thanks
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