Campbell Scientific CR1000 Measurement and Control System - Manual (Page 269)

Section 7. Installation
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CFM100 modules. The card must only be ejected after the status light shows a
solid green.
Q: Why are individual files limited to 2 GB?
A: In common with many other systems, the datalogger natively supports signed-
4-byte integers. This data type can represent a number as large as 231, or in terms
of bytes, roughly 2 GB. This is the maximum file length that can be represented
in the datalogger directory table.
Q: Why does a large card cause long program compile times?
A: Program compile times increase with card and file sizes. As the datalogger
boots up, the card must be searched to determine space available for data storage.
In addition, for tables that are created by TableFile() with
Option 64 , an empty file
that is large enough to hold all of the specified records must be created (i.e.,
memory is pre-allocated). When using TableFile() with
Option 64 , program
compile times can be lessened by reducing the number of records or data interval
that will be included in each file. For example, if the maximum file size specified
is 2 GB, the datalogger must scan through and pre-allocate 2 GB of CF card
memory. However, if smaller files are specified, then compile times are reduced
because the datalogger is only required to scan through enough memory to pre-
allocate memory for the smaller file.
Q: Why does a freshly formatted card cause long compile times?
A: Program compile times take longer with freshly formatted cards because the
cards use a FAT32 system (File Allocation Table with 32 table element bits) to be
compatible with PCs. To save time, use a PC to format CF cards. After
formatting the card, write any file to the card, then delete the file. This action sets
up the card for faster initial use.
FAT32 uses an “info sector” to store the free cluster information. This info sector
prevents the need to repeatedly traverse the FAT for the bytes free information.
After a card is formatted by a PC, the info sector is not automatically updated.
Therefore, when the datalogger boots up, it must determine the bytes available on
the card prior to loading the Status table. Traversing the entire FAT of a 16 GB
card can take up to 30 minutes or more. However, subsequent compile times are
much shorter because the info sector is used to update the bytes free information.
To avoid long compile times on a freshly formatted card, format the card on a PC,
then copy a small file to the card, and then delete the file (while still in the PC).
Copying the file to the freshly formatted card forces the PC to update the info
sector. The PC is much faster than the datalogger at updating the info sector.
Q: Which CF memory card should I use?
A: Campbell Scientific recommends and supports only the use of FMJ brand CF
cards. These CF cards are industrial-grade and have passed Campbell Scientific
hardware testing. Following are listed advantages FMJ brand CF cards have over
less expensive commercial-grade cards:
• less susceptible to failure and data loss
• match the datalogger operating temperature range
• faster read/write times