HP-UX Memory File System (MemFS) 2.0

Introducing HP-UX Memory File System (MemFS)
Design Limitations
Chapter 112
Design Limitations
MemFS uses the Hierarchical File System (HFS) as its base, and, as a result, inherits several
HFS functions that increase usage overhead. This includes the overhead of a disk based file
system structure, static allocation, and pre-initialization of inodes. Also, lack of kernel
pageable memory in HP-UX 11i v2 creates a requirement to pre-allocate user memory at
mount time, increasing memory requirements for MemFS. These limitations will be
addressed in a future MemFS version.
Known Problems
• MemFS stores all metadata and data in the buffer cache. If a large number of MemFS
files and file systems are created, the buffer cache gets filled by the MemFS buffers
causing the other file systems to under perform as the buffer cache used by all the file
systems is common.
• On large memory usage of MemFS file system instances, such as when MemFS pages
occupy memory equal to the total RAM, the system may experience slow responses.
Other Limitations
• Since many HP-UX applications store critical data in /tmp, not being able to recover /tmp
can cause serious damage to the consistency of such applications. HP recommends that
you must not use MemFS to mount /tmp and any file systems which contain critical data
that require consistency.
A limitation with MemFS and Ignite-UX (and other products) is that there is no support
for /tmp or for /var/tmp as MemFS file systems. MemFS file systems should be used only
to hold application transient files. The file system and all its contents will be lost with an
unmount or reboot. Ignite-UX uses the information stored in /tmp during the install
process and therefore the /tmp file systems cannot be MemFS based.