Modify Cache Parameters

Overview

This function changes the cache parameters of each volume.

Performance of the storage system varies depending on the cache hit ratio. The storage system detects sequentiality when a host requests Read/Write. If sequentiality is detected when a Read request is issued, the cache hit ratio is improved by reading the sequential data into the cache memory in advance. The characteristics of Read/Write requests from the host depends on the system. Performance of the storage system may improve by specifying a cache parameter that is suitable for the system that is being used.

The parameters to specify are as follows:

Cache Page Capacity

Specify the cache capacity that is used by volumes.
Prefetch Limit (PL)

Specify the value to calculate the amount of data that is to be read from the drive in advance (amount of data to prefetch from the drive) when the cache detects the sequentiality of data access (Read I/O).
Force Prefetch Mode (FP)

Specify whether to perform prefetch even if the sequentiality of data access (Read I/O) is not detected.
Multi Writeback Count (MWC)

Specify the number of processes that can be written back at the same time.
Prefetch Sequential Detect Count (PSDC)

Specify the number of times for sequential data detection to determine the sequentiality of data access (Read I/O).
Sequential Dirty Detect Count (SDDC)

Specify the number of times for sequential data detection to determine the sequentiality of data access (Write I/O).
Sequential Slope (SS)

A parameter to determine the sequentiality of data access (Read I/O). Specify the number of LBAs by which the previous I/O and the current I/O are considered as sequential data.
Sequential Dirty Slope (SDS)

A parameter to determine the sequentiality of data access (Write I/O). Specify the number of LBAs by which the previous I/O and the current I/O are considered as sequential data.
Sequential Parallel Multi I/O Count (SPMC)

A parameter to determine the sequentiality of data access (Read I/O and Write I/O). Specify the number of I/Os by which the previous I/O and the current I/O are considered as sequential data.
Extreme Cache

Specify whether to "Enable" or "Disable" Extreme Cache for the volumes (for the ETERNUS DX500 S5/DX600 S5/DX900 S5 and the ETERNUS DX8900 S4).
Extreme Cache Pool

Specify whether to "Enable" or "Disable" Extreme Cache Pool for the volumes (for the ETERNUS DX100 S5/DX200 S5).

Caution

For TPV, specify the MWC for each TPP. Refer to the [Modify Cache Parameters (TPP)] function for details.
Cache parameters cannot be changed when pinned data exists in the storage system.
Cache parameters for Deduplication/Compression Volumes cannot be specified.
Do not set the cache parameters for the External Volumes (or volumes whose "Usage" is "Migration").

Note

The same cache parameter can be applied for multiple volumes in a single operation.

User Privileges

Availability of Executions in the Default Role

Default role	Availability of executions
Monitor
Admin
StorageAdmin
AccountAdmin
SecurityAdmin
Maintainer

Refer to "User Roles and Policies" for details on the policies and roles.

Settings

In this screen, change the cache parameters. Refer to "Volume Types for Which Cache Parameters Should Be Specified" for the volume types for which the parameters should be specified.

Parameters Setting

Item

Description

Setting values

Cache Page Capacity

Specify the cache capacity that is used by volumes.

When "-" (hyphen) is selected, the cache capacity is not limited. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, a "-" (hyphen) is displayed for the field.

(Advantage of limiting the cache capacity)

If volumes with a high I/O load exist, data in a low I/O load volume may not be stored in the cache memory and the cache hit ratio for the low I/O load volume is reduced. By limiting the cache capacity that is used by high I/O load volumes, a reduction in performance when low I/O load volumes are accessed can be prevented.

(Disadvantage of limiting the cache capacity)

The cache hit ratio for high I/O load volumes is lowered and the access performance for the volumes may be reduced.

Caution

Note that this parameter is not used to specify the capacity of dedicated cache for the relevant volume. This parameter limits the cache capacity that can be used for the relevant volume. Although a volume with this parameter cannot use a cache memory that exceeds the specified value, other volumes can use the entire cache, which includes the specified capacity.
The cache page capacity must be changed when the I/O load of the volume is low.
If write data in the cache memory exceeds the specified cache page capacity for a volume, the cache page capacity cannot be changed.
The cache page capacity cannot be changed for concatenated volumes that are created by the LUN Concatenation function.
The specified cache page capacity includes the mirror area. Note that the maximum cache capacity used by read I/O is a half the specified value.
When the cache page capacity is limited, the capacity cannot be expanded for the relevant volume. Reset the cache page capacity to the default value before expanding the volume capacity.
If the cache page capacity is set, Extreme Cache and Extreme Cache Pool of the specified volume are not used (the enabling/disabling of the Extreme Cache and Extreme Cache Pool settings is not changed).

"-" (hyphen) (Default)

32.50 MB

65.00 MB

130.00 MB

260.00 MB

520.00 MB

1040.00 MB (*1)

2080.00 MB (*2)

*1	:	This item cannot be selected for the ETERNUS DX60 S5.
*2	:	This item cannot be selected for the ETERNUS DX60 S5/DX100 S5.

Prefetch Limit (PL)

Specify the prefetch limit of the volume.

If "0" is specified for the "Prefetch Limit (PL)", data prefetch is not performed. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(Advantage of specifying a large value)

When specifying larger PL, the amount of data that is read from a drive for a single read process is increased. As a result, the number of times that data needs to be read (Staging) from the drive is reduced.

(Disadvantage of specifying a large value)

When a large "Prefetch Limit" value is specified, the amount of data that is read from a disk for a single read process is increased. As a result, the amount of data that is read (Staging) from the disk for a single read process increases and requested data may not be read before the next read or write request from the host is issued.

0 - 64

8 (Default)

Blank

Force Prefetch Mode (FP)

Select whether to enable (ON) or disable (OFF) the Force Prefetch Mode to forcibly fetch the cache in advance. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, "OFF" is selected for the field.

This setting is required to improve the sequential read access performance.

(Advantage when the "Force Prefetch Mode" is "ON")

When a number of sequential accesses are performed for one volume, the storage system may regard as random accesses occurs. By selecting "ON" for "Force Prefetch Mode", prefetching is forcibly performed in such a case.

(Disadvantage when the "Force Prefetch Mode" is "ON")

For random read access, unnecessary data is read from the drive and random read access performance may be reduced.

OFF (Default)

ON

Multi Writeback Count (MWC)

Specify the value of the Multi Writeback Count. It is not necessary to change the default value for normal use.

The Multi Writeback Count cannot be specified for volumes that are concatenated by the LUN Concatenation function.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(Advantage of specifying a large value)

When specifying larger MWC, sequential write access performance is improved. Note that this is not effective when a number of random write accesses occur.

(Disadvantage of specifying a large value)

Depending on the ratio of read access and write access, read access performance may be reduced.

Note

The setting values available for Multi Writeback Count vary depending on the RAID level and drive configuration. Refer to "Allowed Input for MWC" for details.

1 - 16

Blank

Refer to "Allowed Input for MWC" for the default value.

Prefetch Sequential Detect Count (PSDC)

Specify the value of the Prefetch Sequential Detect Count. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(Advantage of specifying a large value)

If the host splits data into multiple pieces and performs read access in succession, the access may be determined as sequential access even if it is actually random access. When specifying larger PSDC, the required number to detect sequential data for determining sequential data access is increased and a reduction in performance due to incorrect prefetch can be avoided.

(Disadvantage of specifying a large value)

Depending on the amount of sequential data, a large PSDC slows the determination of sequential data access and performance may be reduced.

1 - 255

5 (Default)

Blank

Sequential Dirty Detect Count (SDDC)

Specify the value of the Sequential Dirty Detect Count. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(Advantage of specifying a large value)

If the host splits data into multiple pieces and performs write access in succession, the access may be determined as sequential access even if it is actually random access. When specifying larger SDDC, the required number to detect sequential data for determining sequential data access is increased and a reduction in performance due to incorrect prefetch can be avoided.

(Disadvantage of specifying a large value)

Depending on the amount of sequential data, a large SDDC slows the determination of sequential data access and performance may be reduced.

1 - 255

5 (Default)

Blank

Sequential Slope (SS)

Specify the value of the Sequential Slope. If the following equation is true for sequential data access (Read I/O), the access is determined as sequential access. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(End LBA of the previous I/O + 1) + Sequential Slope (SS) ⊇ Start LBA of the current I/O

(Advantage of specifying a large value)

The following access can be also determined as sequential access.

A sequential access that does not have successive LBAs.
A sequential access that issues multiple host I/Os at the same time and is unable to be received in the order of LBAs.

(Disadvantage of specifying a large value)

A larger SS may cause random access to be determined as sequential access, resulting in reduced performance due to incorrect prefetching.

0 - 4096

128 (Default)

Blank

Sequential Dirty Slope (SDS)

Specify the value of the Sequential Dirty Slope. If the following equation is true for sequential data access (Write I/O), the access is determined as sequential access. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(End LBA of the previous I/O + 1) + Sequential Dirty Slope (SDS) ⊇ Start LBA of the current I/O

(Advantage of specifying a large value)

The following access can be also determined as sequential access.

A sequential access that does not have successive LBAs.
A sequential access that issues multiple host I/Os at the same time and is unable to be received in the order of LBAs.

(Disadvantage of specifying a large value)

A larger SDS may cause random access to be determined as sequential access, resulting in reduced performance due to incorrect prefetching.

0 - 4096

128 (Default)

Blank

Sequential Parallel Multi I/O Count (SPMC)

Specify the value of the Sequential Parallel Multi I/O Count. It is not necessary to change the default value for normal use.

If multiple volumes with different settings are selected and [Modify Cache Parameters] is clicked, the field is blank.

(Advantage of specifying a large value)

If data access (Read I/O and Write I/O) for the large sequential area is divided into multiple commands and issued at once, the I/O processing order may be changed in the CM and access may be considered as non-sequential access. SPMC is used to determine if there is an I/O whose LBA (of the starting address) starts within the specified value from the previous I/O is sequential access. Compared with "SS" and "SDS" which determines the sequential access by LBA numbers, SPMC can be used for large I/Os.

(Disadvantage of specifying a large value)

A larger SPMC may cause random access to be determined as sequential access, resulting in reduced performance due to incorrect prefetching. Also, SPMC is not expected to have an effect on data access with multiple I/O sizes.

0 - 32

The default value varies depending on the model.

ETERNUS DX60 S5: 2

ETERNUS DX100 S5: 4

ETERNUS DX200 S5: 8

ETERNUS DX500 S5: 8

ETERNUS DX600 S5: 12

ETERNUS DX900 S5: 12

ETERNUS DX8100 S4: 8

ETERNUS DX8900 S4: 12

ETERNUS AF150 S3: 4

ETERNUS AF250 S3: 8

ETERNUS AF650 S3: 12

Blank

Extreme Cache

Select whether to "Enable" or "Disable" the Extreme Cache. It is not necessary to change the default value for normal use.

If multiple volumes are selected when starting this function and different Extreme Cache settings have been specified for each volume, "Enable" is selected for this item.

This item is displayed when Extreme Cache is enabled for the storage system.

Caution

Extreme Cache is supported in the ETERNUS DX500 S5/DX600 S5/DX900 S5 and the ETERNUS DX8900 S4. Note that "Extreme Cache" and "Current Extreme Cache" are not displayed for the other models.
When selecting volumes that cannot use this parameter as the target of this function, this item is not selected and cannot be specified.
The Extreme Cache setting for the following volumes are fixed to "Disable" and cannot be changed.
- Volumes that are created in a RAID group configured with SSDs or SSD SEDs (Standard, Standard (LUN Concatenation), and WSV)
- Volumes that are created in a TPP configured with SSDs or SSD SEDs (TPV)
- ODX Buffer volumes

Enable (Default)

Disable

Extreme Cache Pool

Select whether to "Enable" or "Disable" the Extreme Cache Pool. It is not necessary to change the default value for normal use.

If multiple volumes are selected when starting this function and different Extreme Cache settings have been specified for each volume, "Enable" is selected for this item.

This item is displayed when Extreme Cache Pool is enabled for the storage system.

Caution

Extreme Cache Pool is supported in the ETERNUS DX100 S5/DX200 S5. Note that "Extreme Cache Pool" and "Current Extreme Cache Pool" are not displayed for the other models.
When selecting volumes that cannot use this parameter as the target of this function, this item is not selected and cannot be specified.
The Extreme Cache Pool setting for the following volumes are fixed to "Disable" and cannot be changed.
- Volumes that are created in a RAID group configured with SSDs or SSD SEDs (Standard, Standard (LUN Concatenation), and WSV)
- Volumes that are created in a TPP configured with SSDs or SSD SEDs (TPV)
- ODX Buffer volumes

Enable (Default)

Disable

Volume Types for Which Cache Parameters Should Be Specified (Should be specified: )

Item	Volume Type
Item	Standard	SDV	SDPV	Standard (LUN Concatenation)	TPV	FTV	WSV
Cache Page Capacity
Prefetch Limit (PL)
Force Prefetch Mode (FP)
Multi Writeback Count (MWC)					(*1)
Prefetch Sequential Detect Count (PSDC)
Sequential Dirty Detect Count (SDDC)
Sequential Slope (SS)
Sequential Dirty Slope (SDS)
Sequential Parallel Multi I/O Count (SPMC)
Extreme Cache
Extreme Cache Pool

*1

:

Specify the parameter for each TPP. Refer to the [Modify Cache Parameters (TPP)] function for details.

Note

The cache parameters for FTVs cannot be set with Web GUI. Use CLI to set the parameters.

Allowed Input for MWC

Allowed Input for MWC When Using the Default Stripe Depth Value

When using the default Stripe Depth value, refer to the following table for the allowed MWC value:

RAID level	Drive configuration (*1)	Allowed input for MWC (Default)
RAID level	Drive configuration (*1)	Stripe Depth = 64 KB (Default)
RAID0	2D	1 - 16 (4)
	3D	1 - 10 (3)
	4D	1 - 8 (2)
	5D	1 - 6 (2)
	6D	1 - 5 (2)
	7D	1 - 4 (2)
	8D	1 - 4 (1)
	9D	1 - 3 (1)
	10D	1 - 3 (1)
	11D - 16D	1 - 2 (1)
RAID1	1D+1M	1 - 16 (8)
RAID1+0	2D+2M	1 - 16 (4)
	3D+3M	1 - 10 (3)
	4D+4M	1 - 8 (2)
	5D+5M	1 - 6 (2)
	6D+6M	1 - 5 (2)
	7D+7M	1 - 4 (2)
	8D+8M	1 - 4 (1)
	9D+9M	1 - 3 (1)
	10D+10M	1 - 3 (1)
	11D+11M - 16D+16M	1 - 2 (1)
RAID5	2D+1P	1 - 8 (4)
	3D+1P	1 - 8 (3)
	4D+1P	1 - 8 (2)
	5D+1P	1 - 6 (2)
	6D+1P	1 - 5 (2)
	7D+1P	1 - 4 (2)
	8D+1P	1 - 4 (1)
	9D+1P	1 - 3 (1)
	10D+1P	1 - 3 (1)
	11D+1P - 15D+1P	1 - 2 (1)
RAID5+0	(2D+1P) × 2	4 (fixed)
	(3D+1P) × 2	2 (fixed)
	(4D+1P) × 2	2 (fixed)
	(5D+1P) × 2 - (15D+1P) × 2	1 (fixed)
RAID6	3D+2P	1 - 8 (3)
	4D+2P	1 - 8 (2)
	5D+2P	1 - 6 (2)
	6D+2P	1 - 5 (2)
	7D+2P	1 - 4 (2)
	8D+2P	1 - 4 (1)
	9D+2P	1 - 3 (1)
	10D+2P	1 - 3 (1)
	11D+2P - 14D+2P	1 - 2 (1)
RAID6-FR	(3D+2P)x2+1HS (3D+2P)x6+1HS	1 - 8 (3)
	(4D+2P)x2+1HS (4D+2P)x5+1HS	1 - 8 (2)
	(5D+2P)x4+1HS	1 - 6 (2)
	(6D+2P)x2+1HS	1 - 5 (2)
	(8D+2P)x3+1HS	1 - 4 (1)
	(9D+2P)x2+1HS	1 - 3 (1)
	(12D+2P)x2+1HS (13D+2P)x2+1HS	1 - 2 (1)

*1

:

D: Data drives, M: Mirror drives, P: Parity drives, HS: Hot Spares

Allowed Input for MWC When the Stripe Depth Value Is Tuned

When the Stripe Depth value is tuned, refer to the following table for the allowed MWC value:

RAID level	Drive configuration (*1)	Allowed input for MWC (Default)
		When the Stripe Depth is ...
		128KB	256KB	512KB	1024KB
RAID0	2D	1 - 8 (4)	1 - 4 (4)	1 - 2 (2)	1 (fixed)
	3D	1 - 5 (3)	1 - 2 (2)	1 (fixed)	1 (fixed)
	4D	1 - 4 (2)	1 - 2 (2)	1 (fixed)	1 (fixed)
	5D	1 - 3 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	6D	1 - 2 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	7D	1 - 2 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	8D	1 - 2 (1)	1 (fixed)	1 (fixed)	1 (fixed)
	9D - 16D	1 (fixed)	1 (fixed)	1 (fixed)	1 (fixed)
RAID1+0	2D+2M	1 - 8 (4)	1 - 4 (4)	1 - 2 (2)	1 (fixed)
	3D+3M	1 - 5 (3)	1 - 2 (2)	1 (fixed)	1 (fixed)
	4D+4M	1 - 4 (2)	1 - 2 (2)	1 (fixed)	1 (fixed)
	5D+5M	1 - 3 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	6D+6M	1 - 2 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	7D+7M	1 - 2 (2)	1 (fixed)	1 (fixed)	1 (fixed)
	8D+8M	1 - 2 (1)	1 (fixed)	1 (fixed)	1 (fixed)
	9D+9M - 16D+16M	1 (fixed)	1 (fixed)	1 (fixed)	1 (fixed)
RAID5	2D+1P	1 - 4 (4)	1 - 2 (2)	1 (fixed)	-
	3D+1P	1 - 4 (3)	1 - 2 (2)	1 (fixed)	-
	4D+1P	1 - 4 (2)	1 - 2 (2)	1 (fixed)	-
	5D+1P	1 - 3 (2)	1 (fixed)	-	-
	6D+1P	1 - 2 (2)	1 (fixed)	-	-
	7D+1P	1 - 2 (2)	1 (fixed)	-	-
	8D+1P	1 - 2 (1)	1 (fixed)	-	-
	9D+1P - 15D+1P	1 (fixed)	-	-	-

*1

:

D: Data drives, M: Mirror drives, P: Parity drives, "-": Stripe Depth expansion is not available

Display Contents

In this screen, detailed information and cache parameter setting information for the selected volume are displayed.

Item	Description
No.	The volume number is displayed.
Name	The volume name is displayed.
Type	The volume type is displayed. Standard WSV TPV FTV SDV SDPV
Current Cache Page Capacity	The value of the current cache page capacity setting is displayed.
Current PL	The value of the current Prefetch Limit setting is displayed.
Current FP	When the Force Prefetch Mode is enabled, "On" is displayed. When the mode is disabled, "Off" is displayed.
Current MWC	The value of the current Multi Writeback Count setting is displayed.
Current PSDC	The value of the current Prefetch Sequential Detect Count setting is displayed.
Current SDDC	The value of the current Sequential Dirty Detect Count setting is displayed.
Current SS	The value of the current Sequential Slope setting is displayed.
Current SDS	The value of the current Sequential Dirty Slope setting is displayed.
Current SPMC	The value of the current Sequential Parallel Multi I/O Count setting is displayed.
Current Extreme Cache	The current Extreme Cache status is displayed. A "-" (hyphen) is displayed for volumes that do not support the Extreme Cache. This item is displayed when Extreme Cache is enabled for the storage system.
Current Extreme Cache Pool	The current Extreme Cache Pool status is displayed. A "-" (hyphen) is displayed for volumes that do not support the Extreme Cache Pool. This item is displayed when Extreme Cache Pool is enabled for the storage system.

Operating Procedures

Select which volume to change the cache parameters for (multiple selections can be made) and click [Modify Cache Parameters] in [Action].
Caution
- [Modify Cache Parameters] cannot be clicked under the following conditions:
  - The usage is "Block/Dedupe&Comp", "Block/Dedupe", "Block/Comp", or "File"
  - The process is "Migration"
  - NAS expanded system volumes are selected
Change the cache parameters and click the [Modify] button.
→ A confirmation screen appears.
Note
- If the [Default] button is clicked before the [Modify] button, the default cache parameters are restored.
Caution
- An error screen appears in the following conditions:
  - Pinned data exists in the storage system
  - The Extreme Cache for the storage system is enabled and the target volume status is not "Available"
Click the [OK] button.

→ The cache parameter modification starts.
Click the [Done] button to return to the screen when starting this function in Step 1.