Dell PowerEdge MX7000 Enclosure: руководство по обслуживанию

Population rules

System modules must be populated as described in the following table:

Table 1. MX7000 population rulesThe table lists the MX7000 population rules.
Category	Maximum population
Blanks	All the empty slots in the MX7000 enclosure must be populated with blanks (Sled, IOM, EC, and PSU). This is required for proper cooling of the enclosure and components.
Fans	All system fans must be populated in the enclosure. Do not to mix Gen 1 (silver grade) fan and Gen 2 (gold grade) fan in the same chassis.
Power supply units	The number of power supply units that are required is dependent upon system configuration and redundancy mode, and the minimum recommended quantity is two. The six PSUs are organized into two groups: Grid A consists of PSUs 1, 2, 3, and Grid B consists of PSUs 4, 5, 6. It is recommended to populate the PSUs in the following order: 1, 4, 2, 5, 3, 6 where an equal number of PSUs on each grid is optimized for Grid Redundancy. PSU redundancy and No Redundancy options do not have any PSU population requirements.
Power cable	AC: One C21/C20 power cable must be connected to the C22 plug corresponding to each populated PSU.
DC power and ground cables	The DC chassis requires special consideration when attaching to site power. Power and ground cables must both use 2AWG wire. NOTE:For information about the DC PSU cabling instructions, please see the Cabling instructions for -48 V to -60 V DC power supply Tech sheet that is shipped together with your DC PSU.
Management module	A Management module must be present to control and manage the enclosure. NOTE:If a single Management module crashes, the system functions normally. NOTE:The enclosure cannot be managed or controlled until the Management module is replaced.
Control panel	The right control panel and one of the left control panel configurations (LCD or LED) must be present on the MX7000 enclosure.
Compute sled	Up to eight single-width or four double-width sleds or a combination can be populated. The double-width sleds must be in slots 1, 3, 5, 7 due to the enclosures design.
Storage Sled	Up to seven Storage sleds can be populated in the enclosure. NOTE:One compute node must be present and it must be mapped to a storage node. One Fabric-C SAS IOM must be present and powered ON.
I/O Module	Only Brocade and SAS IOM are supported in Fabric-C.
	Only one type of IOM can be offered in Fabric-C (Fibre Channel or SAS IOM, not mixed).
	Only one type of switch can be offered in Fabric-B (HPCC or Ethernet).
	Two Fabric-C SAS IOMs must be installed if the enclosure contains a Storage Node.
	Mix Speed of pass-through in same fabric is not enabled.
Mezzanine cards	If the enclosure contains a storage node, Fabric-C MiniMezzanine card (HBA330 or Jumbo PERC) must be installed in one compute node.
	Dual Port or quad port mezzanine cards must be installed for redundant IOM/Pass-through configurations.
	The second processor must be installed on the compute node to support Fabric-B Mezzanine / IOM and Fabric-C Mezzanine / IOM.

MX Infrastructure Thermal Management feature for MX760c sleds tech sheet

This tech sheet provides information about PowerEdge thermal and power optimization for MX7000 with MX760c for customers who purchased MX760c sled after-point-of-sale (APOS) and installs it in an MX7000 chassis with sled configuration requiring a thermally optimized chassis.

MX760c configurations that require a thermally optimized chassis will have a specific component on the order.

Table 1. MX760c component configurations that require a thermally optimized chassis This table describes the component configurations that require a thermally optimized chassis for MX760c :
Component	description
SKU 389-EEXH	High Performance Component
MOD MDW67	MOD, INFO, HIGH PERFORM COMPONENT

MX7000 chassis upgrade requirement:

MX7000 Gold Grade (Hardware version 2, Gen2) fans (customer kit PN: H2YC5/SKU: SKU 750-ADWN; included in MX solutions orders with MX760c)
OME-M (OpenManage Enterprise - Modular) FW 2.00.00.
(scan the QR code to download the firmware)
iDRAC FW 05.10.25/06.10.05
(scan the QR code to download the drivers on sleds installed in MX7000 chassis)
Enterprise Infrastructure Planning Tool (EIPT)
(scan the QR code to access the EIPT)

NOTE: When selecting or upgrading the system configuration, to ensure optimum power utilization, verify the system power consumption with the Enterprise Infrastructure Planning Tool available at Dell.com/calc.

NOTE:To generate the thermally optimized sled-to-slot assignments, enter the MX configuration in the EIPT tool and click Optimize

To setup the sled:

Power off the MX7000 chassis.
Install the eight, MX760c sleds at the front of the enclosure.
Install the four, 60 mm gold grade (Gen 2) fans at the front and the five, 80 mm gold grade (Gen 2) fans at the rear of the MX7000 chassis.
To verify if correct gold grade fans are installed, use one of the following methods:

Physical Verification:

Identify the Gold Grade silksreen on the fan module

Remote verification via OME-M API:

Open a browser and type this URL - https://<your chassis management IP>/api/DeviceService/ Devices
Press Ctrl+F to find the first instance of "ChassisId"
Replace the Devices number in this URL: https://<your chassis management IP>/api/DeviceService/ Devices(<ChassisId>)/InventoryDetails('chassisFansList') and press Enter to view the fan hardware version.

Remote verification via OME-M GUI:

Click MM GUI >Hardware > Fans
Results Gold Grade fans are shown under Hardware Version as 2.
Results Silver Grade fans are shown under Hardware Version as 1.

NOTE: Silver Grade fans do not have "Silver" silkscreen on fan assembly

NOTE: For more information, go to https://www.dell.com/poweredgemanuals>Modular Infrastructure>Upgrade Kits>MX Infrastructure Thermal Management features for MX series sleds

PSU redundancy and population rules

The number of PSUs required depends on the enclosure configuration and redundancy required. The minimum requirement is two PSUs. The enclosure supports one of the following redundancy modes:

No redundancy: This mode distributes the enclosure power load across all PSUs. There are no specific PSU population requirements for No redundancy. The intent of this mode is to have the highest possible limit for power enablement of devices that are added to the enclosure. If there are single or multiple PSU failures, then the enclosure limits performance to operate within the power capabilities of the remaining PSUs.
Grid redundancy: This mode distributes the enclosure power load across all PSUs. The six PSUs are organized into two groups: Grid A consisting of PSUs 1, 2, 3, and Grid B consists of PSUs 4, 5, 6. For grid redundancy, PSUs should be populated in the following order: 1, 4, 2, 5, 3, 6. The grid with the largest PSU capacity determines the limit for power enablement of devices that are added to the enclosure. If there is a grid or PSU failure, then the enclosure power is distributed among the remaining PSUs with the intent that a single healthy grid will continue to provide power to all the components in the system which can experience varied performance depending on the workload.
PSU redundancy: This mode distributes the enclosure power load across all PSUs. There are no specific PSU population requirements for PSU redundancy. PSU redundancy is optimized for a population of six PSUs, and the enclosure limits the power enablement of devices to fit within five PSUs. If there is a single PSU failure, then the enclosure power is distributed among the remaining PSUs to provide power to all the components in the system which can experience varied performance depending on the workload. If there are fewer than six PSUs, then the enclosure limits the power enablement of devices to fit within all populated PSUs. If there is a single PSU failure, then the enclosure limits performance to operate within the power capabilities of the remaining PSUs.

Table 1. PSU population rulesThis table lists the PSU population rules.
PSU count	Population order
2	1, 4 (Optimized for Grid Redundancy 1+1, and Hot Spare)
3	1, 4, 2
4	1, 4, 2, 5 (Optimized for Grid Redundancy 2+2, and Hot Spare)
5	1, 4, 2, 5, 3
6	1, 4, 2, 5, 3, 6 (Optimized for Grid Redundancy 3+3, PSU Redundancy 5+1, and Hot Spare)

Hot Spare: The MX7000 PSUs support the Hot Spare feature with three PSU pairs. This feature enables a PSU pair to have one active PSU and one PSU in sleep mode while the enclosure power consumption is low, and the three PSU pairs meet all the power requirements for the enclosure. This enables efficient power utilization when the overall enclosure power requirement is low. The partner PSU wakes the paired PSU from sleep mode by sending a WAKE signal when the enclosure power requirement increases. The PSU pairs for MX7000 are—1 & 4, 2 & 5, and 3 & 6.

Chassis dimensions

This image shows dimensions of the PoweEdge MX7000 enclosure. — Figure 1. Dimensions of thePowerEdgeMX7000

Table 1. Dimensions of thePowerEdgeMX7000This table gives details of the dimensions of the PowerEdgeMX7000:
Description	Dimension
Xa	482 mm (18.98 inches)
Xb	445 mm (17.52 inches)
Y	307.4 mm (12.11 inches)
Zb	811.6 mm (31.96 inches)
Zc	816.6 mm (32.15 inches)

Chassis weight

Table 1. Chassis weightThe following table shows the maximum weight of the MX7000 enclosure:
Enclosure	Minimum weight	Maximum weight (fully populated)
PowerEdge MX7000	82 kg (180 lb)	182 kg (400 lb)

Fan specifications

The PowerEdge MX7000 enclosure supports four front accessible hot-swap cooling fans and five rear accessible hot-swap cooling fans (Gen 2 fans are required). The cooling fan assembly ensures that the key components of the server such as the sleds, Fabrics, and I/O modules get adequate air circulation to keep them cool. A cooling fan failure can result in overheating and may lead to damage.

Table 1. Supported fansThis table lists the supported fans.
Fan location	Front	Rear
Size	60 mm	80 mm
Number of fans	4	5
Redundancy	3+1	4+1

NOTE:Do not to mix Gen 1 (silver grade) fan and Gen 2 (gold grade) fan in the same chassis.

PSU specifications

The PowerEdge MX7000 enclosure supports up to six AC or DC power supply units (PSUs).

Table 1. PSU specifications
NOTE:
This table lists the specifications of the 3000W power supply.
Description	Specification
PSU	6 x 3000 W AC
Class	Platinum
Heat dissipation (maximum)	1205 BTU/hr
Frequency	50/60 Hz
Voltage	100–240 V AC, autoranging
Current	6 x 16 A for AC input 6 x 83.2 A for DC input
Inrush current (AC)	Maximum 40 A per power supply for 10 ms or less Maximum 50 A per power supply for 1.2 ms or less
Connector	AC connector

CAUTION:Mixed high line and low line AC inputs in the same enclosure is not supported.

NOTE:Heat dissipation is calculated using the PSU wattage rating.

NOTE:In an ideal input voltage condition and over the entire enclosures ambient operating range, the AC inrush current may reach 120 A per power supply for 10 ms or less.

NOTE:This enclosure is also designed to connect to the IT power enclosures with a phase-to-phase voltage not exceeding 240 V.

USB ports

The PowerEdge MX7000 enclosure supports two Type A, USB 2.0 ports on the front panel.

Mini DisplayPort

The PowerEdge MX7000 enclosure supports one Mini DisplayPort (mini DP) on the front panel.

NOTE:You must use a mini DP dongle to connect the enclosure to a VGA display.

PowerEdge MX modules ports and connectors

PowerEdge MX760c

Table 1. PowerEdge MX760c externally accessible connectorsPowerEdge MX760c externally accessible connectors
Connector	Description
USB ports	One USB 3.0-compliant port on the front of the sled. One micro USB 2.0-compliant port for iDRAC Direct on the front of the sled. NOTE:The micro USB 2.0-compliant port on the front of the sled can only be used as an iDRAC Direct port.

PowerEdge MX750c

Table 1. PowerEdge MX750c externally accessible connectorsPowerEdge MX750c externally accessible connectors
Connector	Description
USB ports	One USB 3.0-compliant port on the front of the sled. One micro USB 2.0-compliant port for iDRAC Direct on the front of the sled. NOTE:The micro USB 2.0-compliant port on the front of the sled can only be used as an iDRAC Direct port.

PowerEdge MX740c

Table 1. PowerEdge MX740c externally accessible connectorsPowerEdge MX740c externally accessible connectors
Connector	Description
USB ports	One USB 3.0-compliant port on the front of the sled. One USB 3.0-compliant internal port. One micro USB 2.0-compliant port for iDRAC Direct on the front of the sled. NOTE:The micro USB 2.0-compliant port on the front of the sled can only be used as an iDRAC Direct port.

PowerEdge MX840c

Table 1. PowerEdge MX840c externally accessible connectorsPowerEdge MX840c externally accessible connectors
Connector	Description
USB ports	One USB 3.0-compliant port on the front of the sled. One USB 3.0-compliant port internal port. One micro USB 2.0-compliant port for iDRAC Direct on the front of the sled. NOTE:The micro USB 2.0-compliant port on the front of the sled can only be used as an iDRAC Direct port.

MX7116n Fabric Expander Module

Table 1. MX7116n Fabric Expander Module externally accessible connectorsMX7116n Fabric Expander Module externally accessible connectors
Connector	Description
Externally accessible connectors	2 QSFP28-DD connections to the MX7116n

MX9116n Fabric Switching Engine

Table 1. MX9116n Fabric Switching Engine externally accessible connectorsThis table lists the MX9116n Fabric Switching Engine externally accessible connectors:
Connector	Description
Externally accessible connectors	12 QSFP28-DD ports that can be configured as: 2 x 40 GbE or 2 x 100 GbE ports for uplinks 8 x 10 GbE or 8 x 25 GbE ports for rack servers 2 QSFP28 uplink ports that can be configured as: 1 x 40 GbE 1 x 100 GbE 2 x 50 GbE 4 x 10 GbE 4 x 25 GbE 2 QSFP28 unified ports that can be configured as: 1 x 40 GbE 1 x 100 GbE 2 x 50 GbE 4 x 10 GbE 4 x 25 GbE 8 x 8/ 16/ 32 GbE Fibre Channel mode

MX9002m Management Module

Table 1. MX9002m Management Module externally accessible connectorsMX9002m Management Module Specifications
Connector	Description
Externally accessible connectors	Two x 1G-BaseT Ethernet ports One x Micro-B USB port

MX5108n Ethernet Switch

Table 1. MX5108n Ethernet Switch externally accessible connectorsMX5108n Ethernet Switch Specifications
Connector	Description
Externally accessible connectors	2 x 100 GbE QSFP28 uplink ports 1 x 40 GbE QSFP+ uplink port 4 x 10GBASE-T uplink ports USB Serial and USB Flash ports

MXG610s Fibre Channel Switch

Table 1. MXG610s Fibre Channel Switch externally accessible connectorsMXG610s Fibre Channel Switch externally accessible connectors
Connector	Description
USB port	One micro USB 2.0-compliant port on the front of the sled.
Fibre Channel transceiver	16 external ports supporting 8/ 16/ 32 Gbps speeds using 8 SFPs and 2 QSFPs.

PowerEdge MX 10GBASE-T Ethernet Pass-Through Module

Table 1. PowerEdge MX 10GBASE-T Ethernet Pass-Through Module externally accessible connectorsPowerEdge MX 10 GbE pass through module externally accessible connectors
Connector	Description
Fibre Channel transceiver	16 external ports supporting 10 GbE connections

PowerEdge MX 25 Gb Ethernet Pass-Through Module

Table 1. PowerEdge MX 25 Gb Ethernet Pass-Through Module externally accessible connectorsPowerEdge MX 25 GbE pass through module externally accessible connectors
Connector	Description
Fibre Channel transceiver	16 external ports supporting 25 GbE connections

Video specifications

The management module supports an integrated Matrox G200eW3 graphics controller with a 16 MB video frame buffer.

Table 1. Supported video resolution optionsThis table describes the supported video resolution options:
Resolution	Refresh rate Hz	Color depth (bits)
1024 x 768	60	8, 16, 32
1280 x 800	60	8, 16, 32
1280 x 1024	60	8, 16, 32
1360 x 768	60	8, 16, 32
1440 x 900	60	8, 16, 32
1600 x 900	60	8, 16, 32
1600 x 1200	60	8, 16, 32
1680 x 1050	60	8, 16, 32
1920 x 1080	60	8, 16, 32
1920 x 1200	60	8, 16, 32

NOTE:1920 x 1080 and 1920 x 1200 resolutions are only supported in reduced blanking mode.

Environmental specifications

NOTE:For additional information about environmental measurements for specific system configurations, see PowerEdge manuals.

Table 1. Temperature specifications When the system is in continuous operation (for altitude less than 950 m or 3117 ft), the temperature specification ranges from 10°C to 35°C (50°F to 95°F) with no direct sunlight on the equipment. When the system is not in operation, the temperature specification is –40°C to 65°C (–40°F to 149°F). For more information about fresh air, see the Expanded Operating Temperature section. The Maximum temperature gradient for both operation and nonoperational systems is 20°C/h (36°F/h). Information about fresh air specification is described in the Expanded Operating Temperature section.
Temperature	Specifications
Storage	–40°C to 65°C (–40°F to 149°F)
Maximum temperature gradient (Operating and storage)	20°C/h (36°F/h)

Table 2. Relative humidity specificationsFor a nonoperational system, the ambient relative humidity ranges from 5% to 95% with 33°C (91°F) maximum dew point. Atmosphere must be noncondensing always. For an operational system, the ambient relative humidity ranges from 10% to 80% with 29°C (84.2°F) maximum dew point.
Relative humidity	Specifications
Storage	5% to 95% RH with 33°C (91°F) maximum dew point. Atmosphere must be noncondensing always.
Operating	10% to 80% RH with 29°C (84.2°F) maximum dew point.

Table 3. Maximum vibration specificationsThe maximum vibration specification of an operational system is0.26 G_rms at 5 Hz to 350 Hz (all axis).The maximum vibration specification of a nonoperational system is 1.88 G_rms at 10 Hz to 500 Hz (vertical axis).
Maximum vibration	Specifications
Operating	0.26 G_rms at 5 Hz to 350 Hz (all axis)
Storage	1.88 G_rms at 10 Hz to 500 Hz (vertical axis)

Table 4. Maximum shock pulse specificationsThe maximum shock specification of an operational system is shock pulses in the positive and negative x, y, and z axis of 6 G for up to 11 ms. The maximum shock specification of a nonoperational system is shock pulses in the positive z axis of 71 G for up to 2 ms and shock pulses in the positive and negative x and y axis of 20 G for up to 7 ms.
Maximum shock pulse	Specifications
Operating	Shock pulses in the positive and negative x, y, and z axis of 6 G for up to 11 ms.
Storage	Shock pulses in the positive z axis of 71 G for up to 2 ms. Shock pulses in the positive and negative x and y axis of 20 G for up to 7 ms.

Table 5. Maximum altitude specificationsThe maximum altitude specification for an operational system is 3048 m (10,000 ft). The maximum altitude specification for a nonoperational system is 12,000 m (39,370 ft).
Maximum altitude	Specifications
Operating	3048 m (10,000 ft)
Storage	12,000 m (39,370 ft)

Table 6. Operating temperature derating specificationIf the operating temperature of a system is up to 35°C (95°F), the maximum temperature reduces by 1°C/300 m (1°F/547 ft) above 950 m (3,117 ft). If the operating temperature of a system is 35°C to 40°C (95°F to 104°F), the maximum temperature reduces by 1°C/175 m (1°F/319 ft) above 950 m (3,117 ft). If the operating temperature of a system is 40°C to 45°C (104°F to 113°F) , the maximum temperature reduces by 1°C/125 m (1°F/228 ft) above 950 m (3,117 ft).
Operating temperature derating	Specifications
Up to 35°C (95°F)	Maximum temperature reduces by 1°C/300 m (1°F/547 ft), above 950 m (3,117 ft).
35°C to 40°C (95°F to 104°F)	Maximum temperature reduces by 1°C/175 m (1°F/319 ft), above 950 m (3,117 ft).
40°C to 45°C (104°F to 113°F)	Maximum temperature reduces by 1°C/125 m (1°F/228 ft), above 950 m (3,117 ft).

Standard operating temperature

Table 1. Standard operating temperature specificationsThe standard operating temperature for altitude less than 950 m or 3117 ft ranges 10°C to 35°C with no direct sunlight on the equipment.
Standard operating temperature	Specifications
Continuous operation (For altitude less than 950 m or 3117 ft)	10°C to 35°C (50°F to 95°F) with no direct sunlight on the equipment.

Expanded operating temperature

Table 1. Expanded operating temperature specificationsWhen the system is in continuous operation, the expanded operating temperature ranges from 5°C to 40°C at 5% to 85% RH with 29°C dew point. NOTE: Outside the standard operating temperature (10°C–35°C), the system can operate continuously in temperatures as low as 5°C and as high as 40°C. For temperatures 35°C to 40°C, derate maximum allowable temperature by 1°C per 175 m above 950 m (1°F per 319 ft). When the system is operating at < 1% of annual operating hours, the expanded operating temperature is –5°C to 45°C at 5% to 90% RH with 29°C dew point. NOTE: Outside the standard operating temperature (10°C–35°C), the system can operate down to –5°C or up to 45°C for a maximum of 1% of its annual operating hours. For temperatures 40°C to 45°C, derate maximum allowable temperature by 1°C per 125 m above 950 m (1°F per 228 ft).
Expanded operating temperature	Specifications
Continuous operation	5°C to 40°C at 5% to 85% RH with 29°C dew point. NOTE:Outside the standard operating temperature (10°C to 35°C), the system can operate continuously in temperatures as low as 5°C and as high as 40°C. For temperatures 35°C to 40°C, derate maximum allowable temperature by 1°C per 175 m (1°F per 319 ft) above 950 m (3,1171 ft).
≤ 1% of annual operating hours	–5°C to 45°C at 5% to 90% RH with 29°C dew point. NOTE:Outside the standard operating temperature (10°C–35°C), the system can operate down to –5°C or up to 45°C for a maximum of 1% of its annual operating hours. For temperatures between 40°C and 45°C, derate maximum allowable temperature by 1°C per 125 m (1°F per 228 ft) above 950 m (3.117 ft).

NOTE:When operating in the expanded temperature range, the performance of the system may be impacted.

NOTE:When operating in the expanded temperature range, ambient temperature warnings may be reported on the LCD panel and in the System Event Log.

Expanded operating range

The operating temperature is specified for a maximum altitude of 950 m for expanded operating range.
Do not perform cold start at 5°C or lower, due to hard drive constraints.
Redundant power supplies are required.

Expanded operating temperature restrictions

For more information about the expanded operating temperature restrictions, see the Installation and Service Manual for the PowerEdge MX sleds at PowerEdge manuals.

Table 1. Expanded operating temperature restrictionsThis table displays the expanded operating temperature restrictions
System	C30	C35	C40E45
Dell PowerEdge MX7000 including the fans, Management Module, and PSUs	No restrictions	No restrictions	No restrictions
Fabrics A and B modules	No restrictions	No restrictions	The MX9116n is not supported.
Fabric C I/O modules	No restrictions	No restrictions	No restrictions

Particulate and gaseous contamination specifications

The following table defines the limitations that help avoid any damages to the IT equipment and/or failure from particulates and gaseous contamination: If the levels of particulates or gaseous pollution exceed the specified limitations and result in equipment damage or failure, you may need to rectify the environmental conditions. Remediation of environmental conditions is the responsibility of the customer.

Table 1. Particulate contamination specifications Air filtration specification: Data center air filtration defines that, ISO Class 8 per ISO 14644-1 should have a 95% upper confidence limit. Note: This condition applies only to data center environments. Air filtration requirements do not apply to IT equipment designed to be used outside a data center, in environments such as an office or factory floor. Note: Air entering the data center must have MERV11 or MERV13 filtration. Conductive dust specification: Air must be free of conductive dust, zinc whiskers, or other conductive particles. Note: This condition applies to data center and nondata center environments. Corrosive dust specification: Air must be free of corrosive dust. Residual dust present in the air must have a deliquescent point less than 60% relative humidity. Note: This condition applies to data center and nondata center environments.
Particulate contamination	Specifications
Air Filtration	Data center air filtration defines that, ISO Class 8 per ISO 14644-1 with a 95% upper confidence limit. NOTE:This condition applies to data center environments only. Air filtration requirements do not apply to IT equipment designed to be used outside a data center, in environments such as an office or factory floor. NOTE:Air entering the data center must have MERV11 or MERV13 filtration.
Conductive dust	Air must be free of conductive dust, zinc whiskers, or other conductive particles. NOTE:This condition applies to data center and nondata center environments.
Corrosive dust	Air must be free of corrosive dust. Residual dust present in the air must have a deliquescent point less than 60% relative humidity. NOTE:This condition applies to data center and nondata center environments.

Table 2. Gaseous contamination specifications The copper coupon corrosion rate is <300 Å/month per Class G1 defines that, ANSI/ISA71.04-1985. The silver coupon corrosion rate is <200 Å/month defines that, AHSRAE TC9.9.
Gaseous contamination	Specifications
Copper Coupon Corrosion	<300 Å/month per Class G1 defines that, ANSI/ISA71.04-1985.
Silver Coupon Corrosion	<200 Å/month defines that, AHSRAE TC9.9.

NOTE:Maximum corrosive contaminant levels measured at ≤50% relative humidity.