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Operating OnLine 3-89
Create a Blobspace
Preliminary Considerations
Verify that the DBSPACES value in the configuration file will not be exceeded.
DBSPACES refer to the total number of blobspaces plus dbspaces.
When you create a blobspace, you specify the blobpage size as a multiple of
the machine-page size.
You specify an explicit pathname for the blobspace. Informix recommends
that you use a linked pathname. (Refer to page 1-22 for further information
about the benefits of using linked pathnames. Refer to page 2-93 for further
information about selecting a chunk pathname. Refer to page 1-43 for guide-
lines on how to determine where your chunks should be located on disk.)
If you are allocating a raw disk device for the blobspace, you might need to
specify an offset to preserve track-0 information used by your
UNIX
operating system. (Refer to page 1-49 for further information about how to
determine if you need an offset.)
If you are allocating cooked disk space, the pathname is a file in a UNIX file
system.
You can mirror the blobspace when you create it if mirroring is enabled for
OnLine. Mirroring takes effect immediately. (Refer to page 4-14 for further
information about the benefits of chunk mirroring.)
If you are logged in as user informix, you can create a blobspace from within
DB-Monitor or from the command line. If you are logged in as root, you must
use the command-line option.
You can create a blobspace while OnLine is in online mode.
Blobpage size can vary among blobspaces. Blobpage size is a multiple of
OnLine page size (specified as BUFFSIZE in the configuration file). You
specify blobpage size as some number of OnLine pages.
Aim to create a blobpage size that is the size of the most frequently occurring
blob. For example, if you are storing 160 blobs and you expect 120 blobs to be
12 KB and 40 blobs to be 16 KB, a 12-kilobyte blobpage size would store the
blobs most efficiently. If speed is your primary concern, use a 16-kilobyte
blobpage so that every blob can be stored on a single blobpage.