VERITAS File SystemÖ 3.5 (HP OnlineJFS/JFS3.5) AdministratorÆs Guide (December 2002)

Chapter 1

The VERITAS File System

Quotas

VxFS supports quotas, which allocate per-user quotas and limit the use of two principal resources: files and

data blocks. You can assign quotas for each of these resources. Each quota consists of two limits for each

resource:

•The hard limit represents an absolute limit on data blocks or files. A user can never exceed the hard limit

under any circumstances.

•The soft limit is lower than the hard limit and can be exceeded for a limited amount of time. This allows

users to temporarily exceed limits as long as they fall under those limits before the allotted time expires.

See “Quota Limits” on page 74 for details on using VxFS quotas.

Support for Databases

Databases are usually created on file systems to simplify backup, copying, and moving tasks and are slower

compared to databases on raw disks.

Using the VERITAS Quick I/O for Databases feature with VxFS lets systems retain the benefits of having a

database on a file system without sacrificing performance. VERITAS Quick I/O creates regular, preallocated

files to use as character devices. Databases can be created on the character devices to achieve the same

performance as databases created on raw disks.

Treating regular VxFS files as raw devices has the following advantages for databases:

• Commercial database servers such as Oracle

Server can issue kernel supported asynchronous I/O calls

(through the asyncdsk or Posix AIO interface) on these pseudo devices but not on regular files.

• read() and write() system calls issued by the database server can avoid the acquisition and release of

read/write locks inside the kernel that take place on regular files.

• VxFS can avoid double buffering of data already buffered by the database server. This ability frees up

resources for other purposes and results in better performance.

• Since I/O to these devices bypasses the system buffer cache, VxFS saves on the cost of copying data

between user space and kernel space when data is read from or written to a regular file. This process

significantly reduces CPU time per I/O transaction compared to that of buffered I/O.

See “Quick I/O for Databases” on page 77 for details on VxFS database support.