In computers with multiple hard drives, a method called staggered spin-up can be employed to prevent the excessive power-consumption of spin-up, which may result in a power shortage. Power consumption during spin-up is often the highest power draw of all of the different operating states of a hard disk drive. Staggered spin-up typically starts one drive at a time, either waiting for the drive to signal it is ready or allowing a predefined period of time to pass before starting the next drive. If the power supply is able to supply sufficient current to start multiple drives at a time, that, too, is common.
Staggered Spin-up (SSU) and Power-Up In Standby (PUIS) are different features that can help control spin-up of multiple drives within a computer system or a disk subsystem. Both are defined in the ATA Specifications Standards. See
Serial ATA for more information.
One feature, called
Power-up in standby (PUIS) (also called PM2
[1]) is used on some Serial ATA (SATA) and Parallel ATA (sometimes called PATA or IDE) hard disk drives. PUIS requires BIOS and/or driver support to use. When power is applied to the hard disk drive, the drive will not spin-up until a PUIS Spin-Up command is issued. The computer system
BIOS or
RAID controller must issue the command to tell the drive(s) to spin-up before they can be accessed. PUIS can be enabled by tools such as
hdparm for drives which support this feature.
Another feature, called Staggered Spin-up (SSU) is used on most Serial ATA (SATA) hard disk drives. This is more common than Power-Up In Standby (PUIS) because it does not require any special commands to get the drive to spin-up. The drive electronics waits for the SATA Data Phy (Physical I/F) to activate to spin-up the drive. The computer system BIOS and/or RAID controller or RAID driver set can delay and control when the different drives will spin-up.
With Western Digital hard disk drives, Pin 11 of the SATA Power Interface controls whether Staggered Spin-Up (SSU) is enabled or not. Pin 11 is also used as an activity LED connection. When the drive is initially powered on, the drive senses whether Pin 11 is left floating (high or '1' logic state) or grounded (low or '0' logic state). SSU is disabled when Pin 11 is grounded. When disabled, the drive will spin-up as soon as power is applied to it. SSU is enabled when Pin 11 is left floating or driven high (high or '1' logic state). The drive will not spin-up until the SATA Phy Interface becomes active with a connection to a SATA controller or SATA RAID controller. The SATA or SATA RAID controller can control when and how many drives can be spun-up. SSU and PUIS are features that are configured in software or
firmware by the manufacturer.
Information from the
Fujitsu Serial ATA Interface for Mobile Hard Disk Drives whitepaper:
[2]
"Staggered spin-up is a simple mechanism by which the storage subsystem controller can sequence
hard disk drive initialization and spin-up. Having this feature not only provides greater reliability, but it allows the system to avoid
power surges if all of the HDDs spin up simultaneously during system power up (in a multi-drive environment). Another benefit to having staggered spin-up is the use of more cost-effective
power supplies, which prevents power supply damage and system
brownouts."
Note that staggered spin-up of disks is a feature of many multi-drive systems using
SATA and
RAID. It is not typically used on mobile platforms.
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