On 11/14/2012 11:14 AM, Michel Jansens wrote:
> I've ordered a new server with:
> - 4x600GB Toshiba 10K SAS2 Disks
> - 2x100GB OCZ DENEVA 2R SYNC eMLC SATA (no expander so I hope no
> SAS/SATA problems). Specs:
> I want to use the 2 OCZ SSDs as mirrored intent log devices, but as the
> intent log needs quite a small amount of the disks (10GB?), I was
> wondering if I can use the rest of the disks as L2ARC?
> I have a few questions about this:
> -Is 10GB enough for a log device?
A log device, essentially, only needs to hold a single
transaction's-worth of small sync writes, so unless you write more than
that, you'll be fine. In fact, DDRdrive's X1 is only 4GB and works just
> -Can I partition the disks (10GB + 90 GB) and use the unused (90GB)
> space as L2ARC?
Yes, you can.
> -If I use the rest of the disks as L2ARC, do I have to mirror the L2ARC
> or can I just add 2 partitions (eg: 2 x 90GB = 180GB)
L2ARC doesn't have mirroring, it's always striped.
> -If I used non mirrored L2ARC, Could something go wrong if one L2ARC
> device failed (pool unavailable,lock in the kernel, panic,...)?
No, an L2ARC only holds non-dirty data from the main storage pool for
quick access, so if a read to an L2ARC device fails (due to it failing,
being removed, or returning bad data), then the read is simply reissued
to the main pool drives transparently (and fault-management kicks in to
handle the problem with the L2ARC, such as taking it offline, etc.).
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