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

  • To: xen-users@xxxxxxxxxxxxx
  • From: Kuba <kuba.0000@xxxxx>
  • Date: Sat, 28 Jun 2014 17:57:58 +0200
  • Delivery-date: Sat, 28 Jun 2014 15:58:34 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>

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

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."



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