SOLVED Sharing storage of an SSD for ZIL device and volume

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Makki

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Sorry for the maybe dumb question:
I've read everything I found, but i'm still unsure:
given a HP Gen8 with 4x4TB I have one slot left to eqip with an SSD for ZIL-cache (which I really want and need, sync NFS, ESX,... read http://www.freenas.org/blog/zfs-zil-and-slog-demystified/ and http://www.freenas.org/blog/a-compl...-design-part-iii-pools-performance-and-cache/ very carefully)

Is it possible and meaningful to put in - lets say a 500GB SSD and use 50GB for ZIL-cache and the remainder as a volume for storage ?
(storage would be blockchain-data, so if lost it just has to resync a few hours, no need to backup that or keep it on RAIDZx)
The problem with the blockchain-stuff is: it needs highest performance to be comfortable but the data is rather "recoverable waste"..

Thanks for any suggestions :)

Michael
 

wblock

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It would not be ZIL, but SLOG. Anyway, think about this for a second. SLOG needs a fast device to be worth it. Using the same device for anything else means that it will have to share bandwidth, reducing performance as SLOG. Some people do it, but if you really need SLOG, it's a mistake. Trying to use one SSD as SLOG for several pools is the same kind of mistake.
 

Makki

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Thanks,

I'm aware of that. (and sorry for the wording ZIL vs SLOG)
I neither really "need" it (its a small Soho-System but I'm think about the same in 2x 16-disk system which I..)
So, before testing it: So it is possible to share the SSD between SLOG and ZVOL? (Disregarding possible bandwith-sharing issues - it's in both cases rather low-volume but it needs to be fast in - very few peaks without stressing the other magnetic spindles all-day-long)

Michael
 

Makki

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Ok, that was my question, so I'll put a very small SLOG SSD into the single remaining slot, done
(and find some othe solution for the ongoing blockchains to hammer on disks..)

Michael
 

Stux

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Yes. But not with the GUI.

If the SLOG is for one pool, and the ssd pool is used for something else, and that something else won’t necessarily be used at the same time as the slogged pool, then it might be okay.

But this is far from optimal.

An alternative might be to use a PCIe NVMe slog.
 

Makki

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I dont want to fiddle around too much, so the NO is okay for me..

An alternative might be to use a PCIe NVMe slog.

Very good point, thanks! didn't even think of that, so I don't "waste" the existing 500GB SSD for slog.
Already ordered adapter, will try..
 
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