[OpenIndiana-discuss] Good SLOG devices?

Ivar Janmaat ijanmaat at xs4all.nl
Wed Mar 2 23:58:07 UTC 2011

Hello Wessel,

I have some limited time right now so I thought why can't I calculate 
the wear with what I know.

Kown values:
Write IOPS per Windows VM = 5
Number of VMs = 100
Write blocks between 4 and 32 KB (lets assume the worst: 32)

MLC: 10.000 write cycles
SLC: 100.000 write cycles

Can I do the following math?

Writen: 5x100x32 = 16 MB/s
Total amount of data which can be written to a MLC: 10.000 x 100 GB 
(capacity) = 1.000.000 GB
Total amount of data which can be written to a SLC: 100.000 x 100 GB 
(capacity) = 10.000.000 GB

Lifetime MLC: MB / 16 MB/s = 723 Days = 2 years
Lifetime SLC: MB / 16 MB/s = 7230 Days = 20 years

So even without testing I think the MLCs are a no go.
I need to test if the real iops are not 10 times higher than I expect 
otherwise the SLC is also a no go.

One other question:
You said that the ZIL is only read on reboot.
But how does the ZIL work then? How is the data transfered / 
synchronized with the real harddisk? Or is that not done at all?

Kind regards,


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