Author Topic: spanned PPU  (Read 2520 times)

Offline b-earl

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spanned PPU
« on: January 06, 2012, 12:41:37 pm »
Is it possible to add spanned PPU's to the Real Time raid?
If yes about when will it be added?
Server HW: Chenbro RM41416 case | Supermicro X11SCZ-F + LSI SAS 9305-16i | i3-8300 | 16 GB DDR4 ECC Ram
Server OS:   Windows Server 2016 (UEFI) on  250 GB Samsung 970 Evo M.2 ssd
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Offline Brahim

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Re: spanned PPU
« Reply #1 on: January 06, 2012, 01:25:12 pm »
1. Unlike Snapshot RAID, you should use your best disks for PPUs in Real-Time RAID.
2. PPU spanning in RT RAID adds additional overhead and risk not present in Snapshot RAID.

Only for the sake of Flexibility, I am going to keep an open mind to enable it in the future. However, it is extremely low priority.

Offline b-earl

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Re: spanned PPU
« Reply #2 on: January 06, 2012, 02:33:50 pm »
Thanks Brahim,
the answer help me in a decision about what HDD to buy.
Thanks have a nice weekend.
Server HW: Chenbro RM41416 case | Supermicro X11SCZ-F + LSI SAS 9305-16i | i3-8300 | 16 GB DDR4 ECC Ram
Server OS:   Windows Server 2016 (UEFI) on  250 GB Samsung 970 Evo M.2 ssd
tRAID 1.1.0 2017.02.11
Backupserver: Supermicro X10SLM-F UEFI + LSI SAS9211-8i IT FW
Server OS: Win 2016 + tRAID

Offline m0t0k0

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Re: spanned PPU
« Reply #3 on: January 12, 2012, 02:39:23 am »

Just an idea but as the PPU drive is useless outside the pool as it has no data just parity. Could it not be beneficial to have a spanned and stripped PPU like RAID 0 (this would destroy the benefit of having the data on two drives as if one died the whole PPU would be lost) but it would improve the speed at which parity could be written?

I ask as you say you want your best performing drives
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Offline Brahim

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Re: spanned PPU
« Reply #4 on: January 12, 2012, 07:45:36 am »
Just an idea but as the PPU drive is useless outside the pool as it has no data just parity. Could it not be beneficial to have a spanned and stripped PPU like RAID 0 (this would destroy the benefit of having the data on two drives as if one died the whole PPU would be lost) but it would improve the speed at which parity could be written?

I ask as you say you want your best performing drives

Well, you could create that RAID 0 outside of FlexRAID and then add it to the pool as PPU.
I would not call the PPU useless though. It is hard not to, but you should think to it as being just as important (if not more) as any of your data drives.

Offline m0t0k0

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Re: spanned PPU
« Reply #5 on: January 13, 2012, 05:27:18 am »
Well, you could create that RAID 0 outside of FlexRAID and then add it to the pool as PPU.
I would not call the PPU useless though. It is hard not to, but you should think to it as being just as important (if not more) as any of your data drives.


Do you think there would be any draw backs from having a RAID 0 set as a PPU (other than if you lose one disk the whole PPU is gone) as in my server I can add a 2 port SATA card this would allow me to hide 2 x 1TB 2.5" drives this is my only upgrade path past a certain point as I'm limited on space this could then free up one of my 3.5" drives for data.

Or would it be better just to have them as a spanned DRU
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Offline Zach

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Re: spanned PPU
« Reply #6 on: April 21, 2012, 01:34:39 pm »
If you want to stripe 2 drives together for a PPU in Raid 0  I don't think it will cause any problems, as the drive shows up as one disk as far as the system is concerned.
The question is how you obtain the Raid 0 I suppose..   Using a cheapo fakeraid or mobo will probably give you some boost,  but if you are doing it for speed then it might also be worth investigating whether using an HBA or more expensive hardware Raid controller with an onboard cache, etc  would be beneficial for you.

As it is,  2 drives on their own being striped together, will give you some kind of boost since the Read/Write load is being distributed between 2 drives.
The only drawback will be if one of the drives dies, then you lose your PPU.    But then it is just a matter of replacing that drive and using your actual data drives sparingly until that is taken care of.

Although I won't be doing RAID 0, when my new case and a few bits arrive, I will have a file server built and I plan on using a spanned PPU as well. (1.5TB + 500gb).   I'm also going to rip my Seagate out of its external case and install that, giving me 5x 2TB drives as well as 2TB of parity.

« Last Edit: April 21, 2012, 01:38:09 pm by Zach »