F5 ARX-VE, Руководство по планированию

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Chapter 1
Site Planning
1 - 28
Important
Choosing a metadata share that is too small or unreliable can seriously
jeopardize managed-volume performance. A poor configuration for the
metadata can possibly lead to metadata corruption. Choose your metadata
shares carefully, as instructed in this section.
You must choose at least one metadata-storage location for each managed
volume. Viable metadata storage options are as follows:
• Metadata-only share for the volume
• Metadata-only share for the namespace
Alternatively, a very large storage volume can host metadata-only shares for
multiple volumes or even multiple namespaces. In general, each managed
volume requires 3-5 gigabytes of storage space for its metadata, so you
should be able to use a 140-gigabyte volume for a total of 28 managed
volumes (140G/5G per managed volume).
If multiple switches use the same metadata-only shares, each switch must
have its own directory tree (for example, /vol/vol1/switch1 and
/vol/vol1/switch2).
The sections below present some considerations in choosing
metadata-storage candidates for a namespace. Use the information in these
sections as guidelines before configuring any namespaces with managed
volumes.
Sizing the Metadata Share
A metadata share requires multiple gigabytes of storage. If a managed
volume’s metadata share falls below 512 megabytes (0.5 gigabytes) of free
space, the volume software sends an SNMP trap and issues a warning to the
syslog. If it falls below 256 megabytes, stronger warnings appear. If it falls
to 128 megabytes or less, the volume is inaccessible to clients until more
free space is added to the share. This insures against metadata corruption.
Each file requires roughly 300 to 800 bytes of metadata, and each directory
requires roughly 2 Kbytes. These numbers vary for each protocol: for
example, the NFSv2 protocol uses a fixed-length 32-byte file handle,
whereas NFSv3 uses a variable length file handle from 8-64 bytes. If the
namespace supports multiple protocols, each file and directory requires
additional metadata for each protocol. The numbers also vary for each file,
since the metadata contains the file name. Use the byte requirements in the
following table for rough estimations. The following table shows the byte
size for each protocol.