Ashwin Lewis
Sleep mode on servers is a topic of interest for many, especially those who want to reduce power consumption and find a quiet solution for overnight use. Servers are typically designed to run 24/7, but some older models can be put into a suspended state, and modern servers can utilise SSDs to reduce power consumption when idle. However, most purpose-built servers do not support sleep modes, and it is generally not recommended to put a server to sleep as it halts system functions and ceases processing capabilities.
What happens if you sleep on a server?
| Characteristics | Values |
|---|---|
| Server sleep mode | Most purpose-built server hardware does not support sleep mode as they are designed to run 24/7. |
| Power consumption | Power consumption when the system is idle is not much, especially if it uses SSDs instead of hard drives. |
| Server wake-up | Wake on LAN (WoL) is possible, but it takes a specially crafted packet, and power-on time is slow. |
| Alternative to sleep mode | ACPI S4 (suspend to disk, or 'hibernate' in Windows) can be used to power off the server when not in use. |
| Server functionality during sleep mode | The server will not be active and will halt all system functions and cease all processing. |
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What You'll Learn
Purpose-built servers don't support sleep mode
Purpose-built servers are designed to run continuously, 24/7, for years and do not support sleep mode. While some servers may have power-saving capabilities, such as slowing down clock and fan speeds when idle, this is not the same as a full sleep mode. Servers typically use the hours when there is less user-generated load (usually at night) to run background jobs like system backups.
Some users have found ways to work around this limitation by using scripts or scheduling tools to shut down and start up the server at specific times. For example, one user puts their server to "sleep" by using a script to shut it down completely at night and then uses a setting in the motherboard to turn it on again at a certain time each day. Another user employs a tool called “Cron” to wake up and shut down their server at specific times, and they connect to a VPN to wake up the server when needed.
It is important to note that these workarounds may not be suitable for all server setups, and there can be drawbacks. For example, one user reported that their server would randomly wake up all the time when using the "wake on LAN" feature. Additionally, another user mentioned that their workaround resulted in a five-minute delay for the server to start up from a fully cold state.
While some older servers may have supported a middle ground between being fully on and off, modern production environments tend to favour "auto-scaling" resources. This means that instead of putting a server to sleep, it can automatically adjust its power usage based on demand. This can be achieved through features like hibernation and automatic log-on capabilities after a traditional shutdown/full startup.
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ACPI S4 and WoL can be used to power off when not in use
ACPI S4 (hibernation) and Wake-on-LAN (WoL) can be used to power off a computer when not in use, saving energy and improving efficiency.
ACPI, or Advanced Configuration and Power Interface, is an open industry standard for power management in computers, including servers. It defines various power states, from the highest power consumption (S0) to the lowest (S5), with S4 corresponding to hibernation. During hibernation, the user session is closed, and the user state is saved, allowing for a faster subsequent boot compared to a full shutdown (S5). This is particularly useful for systems with limited storage capabilities.
WoL, on the other hand, is a networking standard that enables a computer to be turned on or awakened from sleep mode by a network message, typically a specially constructed Ethernet packet called a "magic packet". WoL can be used to initiate a boot process remotely, even if the computer is communicating via Wi-Fi, by employing the Wake on Wireless LAN (WoWLAN) standard.
By combining ACPI S4 and WoL, a server can be configured to enter a low-power hibernation state when not in use, and then be powered on remotely as needed. This approach not only reduces power consumption during inactivity but also provides the flexibility to activate the server on demand.
To implement this strategy, ensure that WoL is enabled in the Power Management section of the BIOS/UEFI setup. Additionally, consider configuring the system to reserve standby power for the network card, even when the system is shut down, to facilitate remote wake-up capabilities. By leveraging ACPI S4 and WoL together, server administrators can effectively manage power usage and maintain responsiveness when the server's resources are required.
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Power consumption when idle is low, especially with SSDs
SSDs are generally very power-efficient, but they can also draw substantial amounts of power under certain conditions. When idle, SSDs consume less power than HDDs, making them an energy-efficient choice. The power consumption of an idle SSD can vary depending on various factors, such as the type of NAND Flash, the size of the DRAM cache, the interface, the speed, and the workload.
The power consumption of an SSD during idle states can range from as low as ~5mW on a laptop to 20-100mW on a desktop with power management. 2.5-inch SATA SSDs consume between 0.25-2 watts when idle, while M.2 PCI-Express NVMe SSDs consume around 0.50-3 watts. High-performance NVMe drives, especially PCIe Gen 4.0 and Gen 5.0 drives, consume the most power during both active and idle states due to their higher data transfer rates and other components.
To optimize power consumption, SSD manufacturers offer various power management features or settings that can transition the SSD to lower power modes when not in active use, such as Power-saving modes and DevSleep. It is also recommended to keep the firmware up-to-date as manufacturers regularly release updates to improve power efficiency. Minimizing disk usage can also help conserve power, as SSDs consume more power when reading and writing data.
While SSDs are more power-efficient than HDDs, they can still generate excessive heat during idle states, which can lead to throttling and impact system performance. Therefore, it is important to monitor SSD power consumption using system monitoring tools or software provided by the manufacturer and take steps to reduce power consumption if needed.
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A server cannot run while the PC is in sleep mode
A server cannot run while a PC is in sleep mode because sleep mode halts all system functions and ceases all processing. Sleep mode is designed to conserve power, and while it keeps the RAM charged so that the computer can start up from where it left off, it cannot perform any other functions.
Servers are designed to run 24/7, and while some older servers may support a middle ground between being on and off, most purpose-built server hardware does not support sleep mode. This is because sleep mode is intended for occasional use, whereas servers are designed for constant use.
If you need a server to run while your PC is asleep, you can consider using a different computer to run the server. Renting space on a shared or dedicated server in a data center is a faster, safer, and more cost-effective option for small servers. Alternatively, you can use a low-powered device, such as a Raspberry Pi, to run the server.
To improve power efficiency, you can use a server with SSDs instead of hard drives. SSDs consume less power when idle and can spin down when not in use, reducing power consumption.
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A separate, low-powered device can be used to run the server 24/7
Servers are typically designed to run 24/7, and this is often a requirement to ensure consistent uptime and build a user base. However, running a server continuously can result in high power consumption, especially when using hard drives instead of SSDs.
To reduce power consumption, one option is to use a separate, low-powered device as the server. This can be achieved by offloading specific tasks to an ultra-low-power machine, such as a Raspberry Pi (RPi), or using a low-power CPU. For example, a Pentium CPU is a good choice if virtual machines (VMs) are not required, as they offer excellent performance for low power consumption. Additionally, newer CPUs generally consume less power, so upgrading to a modern CPU can help reduce power usage.
Another strategy is to keep the disk on standby and minimise RAM usage, as these components contribute significantly to power consumption. Using SSDs instead of hard drives can also reduce power consumption, as SSDs spin down when idle, resulting in lower power usage.
Some users have reported success with low-power setups, such as using AMD G-series mini PCs, which idle at less than 10W each, or a NUC11ATKPE, which idles around 8W. These low-power options can be further enhanced by combining them with solar panels and battery arrays to achieve self-powered setups.
By employing these strategies and utilising low-power hardware, it is possible to run a server 24/7 while minimising power consumption and maintaining the required uptime.
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Frequently asked questions
Servers are designed to run 24/7 for years, so sleeping on one would not be a good idea. It is possible to enable sleep mode on some servers, but this is not a common feature as it does not make sense for the typical use of a server.
Most purpose-built server hardware does not support ACPI S1, S2, or S3 states, which are what Windows refers to as 'sleep'.
An alternative to sleep mode is to use ACPI S4 (hibernate) to completely power off the server when it is not needed.
For a recent server, power consumption when idle may not be much, especially if using SSDs instead of hard drives. Taking the Dell R530 as an example, it uses 130w of power when on and 35w when powered off.
