I/O Subsystem Requirements

This section contains these topics:

• About the I/O Subsystem

• Rough Estimates of Disk Space Requirements

• Detailed Calculations of Disk Space Requirements

About the I/O Subsystem

The I/O subsystem can be compared to a pump that pumps data to the CPUs to enable them to execute workloads. The I/O subsystem is also responsible for data storage. The main components of an I/O subsystem are arrays of disk drives controlled by disk controllers.

It is important to consider performance requirements when you size the I/O subsystem, rather than size based only on storage requirements. Although disk drives have increased in size, the throughput--that is, the rate at which the disk drive pumps data--has not increased in proportion. In sizing calculations for the I/O subsystem, you should use the following factors as input:

• The size of the database

• The number of CPUs on the system

• An initial estimation of the workload on the Oracle Internet Directory

• The rate at which the disk can pump data

• Space needed to stage data prior to load

• Space needed for index creation and sort activities

Given a range of I/O subsystems, you should always opt for the highest throughput drives. Typically, one can maximize the I/O throughput by one or more of the following techniques:

• Striping logical volumes so that the I/O operations use multiple disk spindles

• Putting different tablespaces in different logical and physical disk volumes

• Distributing the disk volumes on multiple I/O controllers

Some guidelines for organizing Oracle Internet Directory-specific data files are provided in Chapter 21, "Tuning Considerations for the Directory". Depending on the tolerance of disk failures, different levels of Redundant Arrays of Inexpensive Disks (RAID) can also be considered.

Assuming that the decision has been made to get the best possible I/O subsystem, we focus the next section on deriving sizing estimates for the disks themselves.

Rough Estimates of Disk Space Requirements

You can use the following table to derive a rough estimate of the overall disk requirement:

Table 20-5  Disk Space Requirements

Number of Entries in DIT	Disk Requirements
100,000	450MB to 650MB
200,000	850MB to 1.5GB
500,000	2.5GB to 3.5GB
1,000,000	4.5GB to 6.5GB
1,500,000	6.5GB to 10GB
2,000,000	9GB to 13GB

The data shown in the previous table makes the following assumptions:

• There are about 20 cataloged attributes.

• There are about 25 attributes for each entry.

• The average size of an attribute is about 30 bytes.

Going back to our example of Acme Corporation, since our directory population is about one million, this would imply that our disk requirements are approximately 4.5 GB to 6.5 GB. Note that the assumptions made for Acme Corporation regarding the number of cataloged attributes are different, but the previous table should give an approximate figure of the size requirements.

Since the directory may be deployed for a wide variety of applications, these assumptions need not necessarily hold true for all possible situations: There might be cases where the size of attributes is large, the number of attributes for each entry is large, extensive use of ACIs has been made, or the number of cataloged attributes is very high. For such cases, we present simple arithmetic procedures in the following section which will allow the planners to get a more detailed perspective of their disk requirements.

Detailed Calculations of Disk Space Requirements

Because Oracle Internet Directory stores all of its data in an Oracle9i database, the sizing for disk space is primarily a sizing of the underlying database. Oracle Internet Directory stores its data in the following tablespaces:

Table 20-6 Tablespaces Used to Store Oracle Internet Directory Data

Tablespace Name	Contents
OLTS_ATTR_STORE	Stores all of the attributes for all entries in the DIT
OLTS_CT_STORE	Stores all the remaining (including user-defined) catalogs and the indexes defined in the catalogs
OLTS_DEFAULT	Stores all of the data pertaining to the administration of the Oracle Internet Directory as well as the data used for replication support
OLTS_SVRMGSTORE	Stores all the tables and indexes required for Oracle Internet Directory Server Manageability
SYSTEM	Required by Oracle9i database for various book-keeping purposes. Typically, its size remains constant at about 300MB.

This section presents simple arithmetic procedures to determine the size requirements of each of the tablespaces shown earlier. All of the size calculations are based on the following variables:

Table 20-7  Variables Used for Size Calculation

Variable Name	Description
num_entries	Total number of entries in the directory
attrs_per_entry	Average number of attributes for each directory entry
avg_attr_size	Average size of the attribute value in bytes
avg_dn_size	Average size of the DN of an attribute in bytes
objectclass_per_entry	Average number of object classes that an entry belongs to
objectclass_size	Average size of the name of each objectclass in bytes
num_cataloged_attrs	Number of cataloged attributes used in the entries
entries_per_catalog	Average number of entries for each catalog table. This is required because not all cataloged attributes will be present in all entries in the DIT.
change_log_capacity	Number of changes that we wish to buffer for replication purposes
num_acis	Overall number of ACIs in the directory
num_auditlog_entries	Number of auditlog entries to store in the directory
db_storage_ovhd	Overhead of storing data in tables. This overhead corresponds to the relational constructs as well as operating system specific overhead. A value of 1.3 for this variable would represent a 30 percent overhead. The minimum value for this variable is 1.
db_index_ovhd	Overhead of storing data in indexes. This overhead corresponds to the relational constructs as well as the operating system specific overhead. A value of 5 for this variable would represent a 400 percent overhead. The minimum value of this variable is 1.
factor_of_safety	Multiplier for accommodating growth and errors in calculations. A value of 1.3 for this variable would represent a 30 percent factor of safety. The minimum value for this variable is 1.
initial_num_entries	Total number of entries that are initially bulk-loaded into the directory
avg_attrname_len	Average size of attribute name, in bytes
num_stats_entries	Number of statistics entries generated by OID Server Manageability when the host DSF attribute 'orclstatsflag' is enables
attrs_per_stats_entry	Average number of attributes for each statistics entry

Using the variables shown in Table 20-7, the size of individual tablespaces can be calculated as follows:

Table 20-8  Size of Individual Tablespaces

Tablespaces Containing Tables	Formula
ATTRSTORE_INDEX_SIZE	num_entries*(attrs_per_entry+6) *10
CATALOG_INDEX_SIZE	entries_per_catalog*num_cataloged_attrs*avg_attr_size*db_index_ovhd +num_entries*objectclass_per_entry*objectclass_size*db_index_ovhd + num_acis*1.5*avg_dn_size*db_index_ovhd + num_auditlog_entries*2*avg_dn_size*db_index_ovhd
CN_SIZE	num_entries*avg_dn_size*db_storage_ovhd
DN_INDEX_SIZE	num_entries*2*(avg_dn_size * 3)
DN_SIZE	num_entries*2*(avg_dn_size+4)
OBJECTCLASSES_SIZE	num_entries*objectclass_per_entry*objectclass_size*db_storage_ovhd + num_auditlog_entries*2*avg_dn_size*db_storage_ovhd
OLTS_ATTR_STORE	(num_entries*(((attrs_per_entry)*(avg_attrname_len+avg_attr_size+22))+6*35)*db_storage_ovhd)+attrstore_index_size
OLTS_BATTRSTORE	6M+(((num_binary_attrs*avg_binval_length)+6*35)*db_storage_ovhd)
OLTS_CT_STORE	(cn_size+objectclasses_size+dn_size+catalog_index_size+dn_index_size)
OLTS_DEFAULT	(change_log_capacity*4*avg_attr_size*db_storage_ovhd*db_index_ovhd) + (initial_num_entries*2*(avg_dn_size+4))
OLTS_SVRMGSTORE	2M+num_stats_entries*((avg_attrname_len+avg_attr_size+20)*(2*attrs_per_stats_entry)*db_storage_ovhd*(orclstatsperiodicity/10)*12)
SYSTEM	300MB

Use the arithmetic operations shown in the preceding table to compute the exact space requirements for a wide variety of Oracle Internet Directory deployment scenarios. The sum of the sizes of each of the tablespaces should yield the overall database disk requirement. One can optionally multiply that by the "factor_of_safety" variable to get a figure that can compensate for unforeseen circumstances.

Going back to our example of Acme Corporation, we can assign values to each of the variables based on the requirements stated in previous sections. The following table illustrates the values of each variable introduced in this section for Acme Corporation.

Table 20-9  Values for Variables Used for Sizing Calculations

Variable Name	Value
num_entries	1,000,000
attrs_per_entry	20
avg_attr_size	32 bytes
avg_dn_size	40 bytes
objectclass_per_entry	5 (each entry belongs to an average of 5 object classes)
objectclass_size	10 bytes
num_cataloged_attrs	10
entries_per_catalog	1,000,000
change_log_capacity	80,000 changes (2 for each user)
num_acis	80,000 ACIs (2 for each user)
num_auditlog_entries	1000
db_storage_ovhd	1.4 (40% overhead)
db_index_ovhd	5.0 (400% overhead)
factor_of_safety	1.5 (50% factor of safety)
initial_num_entries	1,000,000
num_stats_entries	5
attrs_per_stats_entry	12
'orclstatsperiodicity'	60 (root DSE attribute)
avg_attrname_len	6

If we now plug these values into the equations described earlier, we get the following values:

Table 20-10  Tablespace Sizes

Tablespace Name	Size in Bytes	Size in MB
OLTS_ATTRSTORE	2,223,000,000	2182
OLTS_CT_STORE	2,328,512,000	274
OLTS_DEFAULT	159,680,000	156
OLTS_SVRMGSTORE	2,701,568	3
SYSTEM	314572800	300
Total Size	5038093862	4920

The previous table shows that the estimated size of the database for Acme Corporation would be about 8.25 GB. If all of the data is being loaded in bulk, then the bulkload tool of Oracle Internet Directory would require an additional 30 percent of space occupied by the database to store its temporary files. For Acme Corporation, this would add about 2.5 GB to the total space requirement.