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doc: Minor edits.

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Signed-off-by: John Wilkins <john.wilkins@inktank.com>
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John Wilkins 2013-02-01 11:30:30 -08:00
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doc/install/hardware-recommendations.rst
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@ -112,9 +112,9 @@ Solid State Drives
One opportunity for performance improvement is to use solid-state drives (SSDs)
to reduce random access time and read latency while accelerating throughput.
Solid state drives cost more than 10x as much per gigabyte when compared to a
hard disk drive, but SSDs often exhibit access times that are at least 100x
faster than a hard disk drive.
SSDs often cost more than 10x as much per gigabyte when compared to a hard disk
drive, but SSDs often exhibit access times that are at least 100x faster than a
hard disk drive.
SSDs do not have moving mechanical parts so they aren't necessarily subject to
the same types of limitations as hard disk drives. SSDs do have significant
@ -138,29 +138,31 @@ performance considerations for journals and SSDs:
so you should ensure that the SSD you choose to deploy will perform equal to
or better than a hard disk drive when writing data. Inexpensive SSDs may
introduce write latency even as they accelerate access time, because
sometimes high performance hard drives can write as fast or faster than SSDs!
sometimes high performance hard drives can write as fast or faster than
some of the more economical SSDs available on the market!
- **Sequential Writes:** When you store multiple journals on an OSD you must
- **Sequential Writes:** When you store multiple journals on an SSD you must
consider the sequential write limitations of the SSD too, since they may be
handling the requests of multiple OSD journals simultaneously.
handling requests to write to multiple OSD journals simultaneously.
- **Partition Alignment:** A common problem with SSD performance is that
people like to partition drives, but they often overlook proper partition
alignment, which can cause SSDs to transfer data much more slowly. Ensure
that SSD partitions are properly aligned.
people like to partition drives as a best practice, but they often overlook
proper partition alignment with SSDs, which can cause SSDs to transfer data
much more slowly. Ensure that SSD partitions are properly aligned.
While SSDs are cost prohibitive for object storage, OSDs may see a significant
performance improvement by storing an OSD's journal on a solid state drive and
the OSD's object data on a separate hard disk drive. The ``osd journal``
configuration setting defaults to ``/var/lib/ceph/osd/$cluster-$id/journal``.
You can mount this path to an SSD or to an SSD partition so that it is not
merely a file on the same disk as the object data.
performance improvement by storing an OSD's journal on an SSD and the OSD's
object data on a separate hard disk drive. The ``osd journal`` configuration
setting defaults to ``/var/lib/ceph/osd/$cluster-$id/journal``. You can mount
this path to an SSD or to an SSD partition so that it is not merely a file on
the same disk as the object data.
One way Ceph accelerates filesystem performance is to segregate the storage of
metadata from the storage of the underlying object data. Ceph provides a default
``metadata`` pool. You will never have to create a pool for metadata, but you
can create a CRUSH map hierarchy for your metadata that points only to a host's
SSD storage media. See `Mapping Pools to Different Types of OSDs`_ for details.
One way Ceph accelerates CephFS filesystem performance is to segregate the
storage of CephFS metadata from the storage of the CephFS file contents. Ceph
provides a default ``metadata`` pool for CephFS metadata. You will never have to
create a pool for CephFS metadata, but you can create a CRUSH map hierarchy for
your CephFS metadata pool that points only to a host's SSD storage media. See
`Mapping Pools to Different Types of OSDs`_ for details.
Controllers
@ -192,7 +194,6 @@ is up to date. See `OS Recommendations`_ for notes on ``glibc`` and
multiple OSDs per host.
Networks
========