SLOG and ZIL check

tio

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Oct 30, 2013
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Currently own a Intel 750 400GB nvme pci express ssd for the proposed SLOG

Also have in my possession a sm951 256GB AHCI which I’d be looking to use for the ZIL

This is mainly to improve performance as my setup is an 8 drive rz2 with 4tb wd reds all hooked up through an sas3008
 

Constantin

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jgreco

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Please feel free to check out


If you are thinking that the SLOG is some sort of cache, it is not. It only "accelerates" sync writes, which are often not necessary for general fileservice.

at that article

In general, please try to prefer local resources. If there's something ZFS-related we're missing, it'd be better to get it here and be a single source for good information. It becomes tricky to play judge about the relative merits of redirecting people off-site to often dodgy information...
 
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NugentS

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SLOG = ZIL or rather ZIL=SLOG, Or to be more accurate the ZIL is written to the SLOG
A SLOG requires:
1. PLP - The Intel does - can't quickly find specs on the SM951. ie if you turn the power off - the data still needs to be there when the power comes back on again
2. Very high endurance as its always written to, and never (in a steady state) read from
3. Very high speed

It only works when the data transaction is synchronous, which is essentially iSCSI & NFS. It will not in any way help with SMB type transactions.
It is not a cache.
Are you sure you know and understand what it does and does not do?

Personally I wouldn't use either of your devices as a SLOG. As a minimum I would use a 32GB Optane M.2 (preferably 2) as a starting point. Even that has "only" got 65,000 IOPS (write). The 900p I use has 500,000 (write)

Oh and listen to the Grinch (@jgreco) - he knows all
 

tio

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Oct 30, 2013
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I seem to have misunderstood the purpose of the SLOG. I generally thought it would help with backups and file transfer to the pool.

I’ll more then likely migrate to a different vdev with sas drives in the future instead utilising raid 10
 
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