2

Can I power two usb drives using USB to satas or do i need a powered USB hub?

  • depends on the power required by SSD's - it's not like all SSD's consume the same power. – Jaromanda X Jul 5 at 23:57
  • usually ssd takes 500mA+, so you need to add up other devices to make sure. – tlfong01 Jul 6 at 1:13
4

The Pi3B+ can supply up to 1.2A total across the 4 USB ports. See Raspberry Pi Power Limitations.

This assumes the Pi power supply is adequate.

Whether this would be adequate for 2 SSD drives, depends on the drives. My experience is that the voltage from the USB ports often falls below that required for power hungry external drives, so a powered hub is desirable.

  • 1
    Good, succinct answer! – Seamus Jul 6 at 13:42
2

Question

For connecting two USB SSD/HDDs, does an Rpi USB Hub need any external power?

Short Answer

I measured the idle current and write current of a 1TB SSD, and a2TB HDD.

SSD's idle current is 0mA, and write current around 180mA

HDD's idle (spinning) current is 170mA, and write current 200mA ~ 380mA

My conclusion is that for hobbyist's python programming projects with casual use of SSD or HDD, there is no need to supply external power to the USB hub. If two SSDs are used for professional projects, it is better to supply external power to the USB hub.

One very good thing about SSD is that it is like a 1TB SD card or 1TB USB stick, there is no need to mount or unmount the HDD. (And SSD's speed of around/up to 500MB/s is 10 times higher than micro SD card!) *Rpi Stretch 9 entertains SSD just like SD card and USB stick, with eject option at the top right corner. So I am going to throw my HDDs into the junk box, and buy more SamSung T5 (250GB should be most cost effective for hobbyists) for my other Rpi3/4s.

ssd vs hdd current rating

Long Answer

Well, it also depends on your SSD/HDD's power requirements. For reference, let me describe how I am using one 2.5", 5,400 rpm, 2TB SeaGate Backup Plus Model SRD00F1 HDD, as shown in the picture below.

usb hdd

I will then consider SSDs which has a much less power requirements.

The popular Seagate Backup Plus HDD series has 1/2/4/5TB versions, and power requirements is within 2W (peak). In other words, the maximum current is around 500mA.

I first tested the HDD using an USB hub without external power, on both Win10 PC and Rpi3B+. I found the following current measurements.

  1. Idle (spinning) current ~= 170mA

  2. Startup and working current ~= 200mA ~ 380mA

I mainly use the HDD for backing up my Rpi Micky Mouse project' python programs, with a total size of much less than 1MB a week. In other words, I only use the backup HDD for perhaps 10 minutes each couple of days. I mostly use an 16GB USB stick for frequent everyday backup, perhaps 10 times an evening.

In order not to draw unnecessary power from the Rpi USB power source, heating up the Rpi, I am doing the following.

  1. I am using a 4 channel USB hub with individual on/off switches, and I switch on power for the USB HDD only when I am going to do backing up, therefore saving 170mA idle current.

  2. I also don't automatically mount the HDD during boot time. I only mount the HDD before backup up, and unmount immediately after backing up. This way avoids carelessly unplugging or freezing Rpi, corrupting the HDD.

I found using one Segate 2TB HDD using USB Hub without external power is good enough for my hobbyist projects.

Of course if I am doing more serious work, using more than two 5TB HDDs say, I will definitely use an externally powered hub.

SSD Power Requirements

Power consumption: SSD vs HDD - superUser.stackExchange

SamSung T5 SSD 250GB/500GB/1TB/2TB = 5V 800mA

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References

  1. Seagate Backup Plus Portable Drive Model SRD00F1

  2. Seagate Backup Plus 2.5" Portable HDD 5400rmp USB 3.0 HDD 1/2/4/5TB - US$62 ~ 138

  3. Rpi External Hard Disk Installation - rpi.org

  4. Amazon Best Sellers in External SSD

  5. Samsung T5 Portable SSD - 1TB USB 3.1 External SSD (MU-PA1T0B/AM) - US$178 3-year warranty

  6. Samsung T5 SSD review - DigitalTrends

  7. Samsung T5 Portable SSD User Manual - SamSung

  8. Raspberry Pi 4 SSD performance analysis - geekyGadgets2019jul09

  9. The Raspberry Pi 4 doesn’t work with all USB-C cables - techCrunch

  10. Raspberry Pi 4 won't work with some power cables due to its USB-C design flaw - zdNet

  11. How many kinds of USB-C to USB-C cables are there? - Benson Leung

  12. What is the purpose of PD_SENSE in the Raspberry Pi 4 power circuit?

  13. What's the role of CC pin in Type-C solution - silabs 206sep26

  14. Your new Raspberry Pi 4 won't power on? USB-C cable problem now officially confirmed

  15. Pi4 not working with some chargers (or why you need two cc resistors - Tyler 2019jun28

  16. Right Charger for Rpi 4

  17. UBS-C [and USB-PD] Explained

  18. Raspberry Pi Boot from USB - Gus 2019jan24

  19. Linux Filesystem Hierarchy Standard

Appendices

Appendix A - Newbie friendly Rpi HDD config notes

Part A - Partition and Format USB Hard Disk

Chinese Windows 10 > Control Panel > System and Security > Partition
and Format Hard Disk

Part B - Rpi External Hard Disk Installation

# List partitions on hard disk
$ sudo lsblk -o UUID,NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL,MODEL

# To find locaction hard disk partition (would find /dev/dsa1)
$ sudo blkid 

# Crete mount point name "mydisk"
$ sudo mkdir /mnt/mydisk

Part C -To set hard disk permissions

$ sudo chown pi:pi /mnt/mydisk
$ sudo chmod 777 /mnt/mydisk

Part D - To mount and umount hard disk

$ sudo mount /dev/sda1 /mnt/mudisk $ sudo umount /mnt/mydisk

Part F - Install exfat and ntf drivers

$ sudo apt-get update $ sudo apt-get install exfat-fuse

$ sudo apt-get update $ sudo apt-get install ntfs-3g

Appendix B - Samsung USB3.1 1TB SSD T5 (MU-PA1T0B/AM) Features

  1. Read-Write speeds of up to 540 MB/s

  2. Top to bottom metal design that fits in the palm of your hand

  3. Optional password protection and AES 256-bit hardware encryption

  4. Includes USB Type C to C and USB Type C to A cables

  5. SamSung T5 SSD 250GB/500GB/1TB/2TB Rating = 5V 800mA

Appendix C - Samsung T5 1TB SSD Setup Notes

  1. The T5 SSD is preformatted using exFAT file system. Windows 10 can readily read and write.

  2. Rpi3B+ Stretch 9 already installed for HDD using the following command: $ sudo apt-get update $ sudo apt-get install exfat-fuse immediately detects T5. No mounting is required.

  3. When using exFAT across multiple operating systems, data writing may become locked and you may only be able to read data. If such problem occurs, you can restore write access by following the instructions below.

Windows OS: When the notice pops up saying that write access is disabled, click “Scan and fix” to perform Check Disk (CHKDSK). If you did shut down the notice without performing Check Disk, you may do it by selecting the drive → Right-click → Properties → Tools → click Check.

Appendix D - uuid, fstab, and auto mounting notes

Rpi External Hard Disk Installation - rpi.org

Mount and Auto-Mount Drives on Raspberry Pi (edit fstab/uuid/gid at 4:41)

uuid on Linux fstab file - 2010spe02

fstab (File Syatem Table) - Wikipedia

The fstab (or file systems table) file is a system configuration file commonly found at /etc/fstab on Unix and Unix-like computer systems. In Linux it is part of the util-linux package.

The fstab file typically lists all available disk partitions and other types of file systems and data sources that are not necessarily disk-based, and indicates how they are to be initialized or otherwise integrated into the larger file system structure.

The fstab file is read by the mount command, which happens automatically at boot time to determine the overall file system structure, and thereafter when a user executes the mount command to modify that structure. It is the duty of the system administrator to properly create and maintain the fstab file.

While fstab is still used for basic system configuration, for other uses it has been superseded by automatic mounting mechanisms.

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  • what an intense answere, take my plus for this – clockw0rk Jul 10 at 12:23
  • @clockw0rk, Thank you very much for your nice words and encouragement. Cheers. – tlfong01 Jul 10 at 12:31

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