Re: [Xen-users] Cheap IOMMU hardware and ECC support importance

[Kuba <kuba.0000@xxxxx>]

W dniu 2014-06-28 14:26, Gordan Bobic pisze:

> No, but it does deprecate the RAID and caching parts of a controller, so
> you might as well just use an HBA (cheaper). Covering the whole stack,
> ZFS can also make much better use of on-disk caches (my 4TB HGSTs have
> 64MB of RAM each. If you have 20 of them on a 4-port SATA card with a
> 5-port multiplier on each port, that's 1280MB of cache - more than any
> comparably priced caching controller. Being aware of FS level
> operations, ZFS can be much cleverer about exactly when to flush what
> data to what disk. A caching controller, in contrast, being unaware of
> what is actually going on at file system level, cannot leverage the
> on-disk cache for write-caching, it has to rely on it's own on-board
> cache for write-caching, thus effectively wasting those 1280MB of disk
> cache.
Out of curiosity - does ZoL take control of the on-disk caches? It seems 
that (for example) FreeBSD's implementation does not:
"The caveat about only giving ZFS full devices is a solarism that 
doesn't apply to FreeBSD. On Solaris write caches are disabled on drives 
if partitions are handed to ZFS. On FreeBSD this isn't the case."
https://wiki.freebsd.org/ZFSTuningGuide

Kuba

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