StorageTek Storage Archive Manager and StorageTek QFS Software samu User Interface GuideRelease 5.4 E48431-02 |
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This chapter groups the samu
commands by task and function. Locate the task that you need to carry out and then see the alphabetical command listings in Chapter 3, "Operator Commands", and Chapter 4, "Service and Support Commands", for more information:
This section lists the samu
operator display commands. Note that each command is a lower-case letter of the alphabet (uppercase letters are described in Chapter 4, "Service and Support Commands".
This section starts with a brief summary of the factors that affect file-system performance, the objectives of performance tuning, and the SAM-QFS features that support tuning efforts. It then links to the commands that control the input/output methods that SAM-QFS supports: Paged (Buffered) I/O, Direct I/O, and Switched I/O.
Disk I/O (input/output) involves mechanical processes that are vastly more time-consuming than other file-system operations. So I/O performance tuning focuses on keeping the mechanical work to the absolute minimum necessary for transferring a given amount of data. This means reducing both the number of separate I/Os per data transfer and the number of seeks operations required to service each I/O.
So the basic objectives of I/O tuning are as follows:
Read and write large blocks of data.
Write blocks in units that align with the sector boundaries of the underlying media, so that the disk controller does not have to read and modify existing data before writing the new data.
Queue up small I/Os in cache and write larger, combined I/Os to disk.
To achieve these objectives, SAM-QFS file systems support three kinds of I/O, each of which addresses a different set of file-system usage patterns.
Paged (Buffered) I/O is the default method because it works well with the usage characteristics of common, general-purpose file-systems. Most file-systems are used by multiple users and applications. Each reads and writes small amounts of data in blocks that often depend on application design rather than on disk sector boundaries. File access tends to be random rather than sequential. When properly configured, paged I/O is ideal for this kind of use. User data is cached in virtual memory pages until the Oracle Solaris kernel writes the data to disk. So users and applications write to and read from cache memory, where random access and small block sizes are less of a problem. Performance-critical, physical reads and writes to and from disk are made in larger, better aligned, more nearly sequential chunks.
Direct I/O addresses limitations of paged I/O that become apparent in file systems are dedicated to particular types of data, such as medical imagery, geological information bases, and real-time surveillance imagery. Generally, users and applications read and write large files sequentially in blocks that align with disk sector boundaries. So paging has no performance advantages. It does, however, impose system overhead and delays the point at which data is securely written from memory to disk—the latter potentially critical in realtime applications. In this situation, direct I/O can significantly improve performance. Data is transferred directly between the local buffer on the application host and the SAM-QFS disk device, with no intermediate delays or additional complication.
Switched I/O is a combination of the other two that works by setting an I/O size threshold for the file system. Paged I/O is used until this threshold is reached. Thereafter, the system automatically switches to direct I/O until the request has been completely addressed. Most small requests are handled before the threshold is reached, so they are read from and written to cache memory and transferred to or from disk asynchronously, in larger, better aligned units. But larger requests are handled directly once the threshold is exceeded, without extra caching overhead.
The following commands let you tune the paged I/O characteristics of SAM-QFS file systems based on file size and usage.
The following samu
commands let you change the default I/O behavior of a specified family set device from paged I/O to direct I/O and vice versa:
The commands below control how sparse files are initialized during direct I/O:
As described above, SAM-QFS can be configured to switch from paged I/O to direct I/O when file reads and/or writes exceed specified thresholds. The commands below enable this feature and define the thresholds:
dio_rd_consec
(Limit the Number of Consecutive Direct Reads)
dio_rd_form_min
(Set the Size of Well-Aligned Direct I/O Reads)
dio_rd_ill_min
(Set the Size of Misaligned Direct I/O Reads)
dio_wr_consec
(Limit the Number of Consecutive Direct Writes)
dio_wr_form_min
(Set the Size of Well-Formed Direct I/O Writes)
dio_wr_ill_min
(Set the Size of Misaligned Direct I/O Writes)
The commands below control the archiving and staging behavior of SAM-QFS file systems:
maxpartial
(Set the Maximum Partial Release Size for the File System)
nohwm_archive
(Do Not Start Archiving at the High Water Mark)
partial
(Set the Default Partial Release Size for the File System)
partial_stage
(Set Partial Stage-Ahead Point for the File System)
release
(Release Archived Data Files and Disable Allocation on a Device)
stage_n_window
(Size the Buffer for Reading Directly from Archival Media)
The following commands control how SAM-QFS coordinates interactions between hosts that share a file system.
aplease
(Set Append Lease Expiration Time for a Shared File System)
lease_timeo
(Set the Unused Lease Timeout for a Shared File System)
maxallocsz
(Set the Maximum Allocation Size for a Shared File System)
minallocsz
(Set the Minimum Allocation Size for a Shared File System)
min_pool
(Set the Minimum Number of Shared File System Threads)
The commands below control how and when a read-only host obtains metadata updates from the metadata server.
The following commands are specific to implementations of Oracle Real Application Clusters (RAC) that store data on SAM-QFS file systems using asynchronous I/O and Solaris Volume Manager mirrored volumes.
The samu
interface includes a number of commands that are designed to help you assist Oracle technical support and service representatives. These handle the following tasks:
The samu
service and support display commands are designated by uppercase letters: C
, D
, F
, I
, J
, K
, L
, M
, N
, P
, R
, S
, T
, and U
. They provide debugging and internal state information that is not generally useful without the assistance of a member of the Oracle technical support staff.