How hot-pluggable are SATA drives?

[smolloy]

I have a system built out of four SATA drives -- two main drives, and two backups. One of the backup drives is permanently mounted, and I backup my system to it every night. The other backup drive is on a neat little removable 5.25inch caddy, that allows me to copy the backup to it, switch it off and slide it out, in order to take it into work to protect me against the possibility of my house burning down. My computer will be destroyed, but my family photos will still exist!!

My question is about hot-plugging this drive. I am able to mount it and write to it if I boot the computer with the drive connected. I then unmount it and physically remove it. However, if I re-insert it I am not able to mount it again. I just get a complaint that "special drive /dev/sdd1 doesn't exist". To get the system to recognise that the drive is there I have to reboot.

Can anyone tell me if SATA drives are hotpluggable in linux, and, if so, how? Do I need a kernel upgrade??

smolloy@linux:~> uname -a
Linux linux 2.6.16.21-0.25-smp #1 SMP Tue Sep 19 07:26:15 UTC 2006 x86_64 x86_64 x86_64 GNU/Linux

[smolloy]

Does anyone know anything about doing this? I.e. how to have my system recognise there is a new device present when I hot-plug the SATA drive, and allow me to mount it without rebooting?

[eraker]

I certainly don't know how to do it, but I was curious, and I found this site:
http://linux-ata.org/software-status.html#hotplug


It had the following note:

Hotplug support
libata supports both controller hotplug ("yank the card") and device hotplug ("yank the drive").

Most SATA controllers are hotplug-capable, if your system bus (PCI, etc.) is also hotplug-capable. All SATA devices are hotplug-capable.

The following SATA controllers will never support hotplug: Intel ICH5-8 (non-AHCI), Pacific Digital Talon (ADMA), Promise SATA SX4.

These controllers do not export enough information about the SATA phy to make it possible to support hotplug. In some cases, such as Intel ICH5-8 (non-AHCI), it is possible to support "coldplug" operation: the user informs the OS driver he wishes to disconnect his SATA device, rather than simply disconnecting it.

[smolloy]

Thanks for that eraker. Looks like SATA hotplug support will be in the 2.6.19 version of the kernel, so I'll just have to be patient

Thanks for finding that for me.

[smolloy]

Looks like 2.6.19 has been released!

I might try it out and see how well the hotplugging is handled.

[apoc123]

I had the same problem like you just last week. I have a marvell Sata Controller, chipset 88SX6081. My Linux distro is Centos 4.4.

It turns out that the Sata driver that comes with Centos 4.4 does not work 100% with my card. Thus although the hotplug event was fired, the driver does not export enough information in order for the kernel to do the work.

When i get the driver from Marvell and recompile it, everything magically works out. Driver is a big piece in the hotplug chain so you may want to take a look.

[smolloy]

Thanks for the tip apoc123.

I found this page that told me that I needed libata's sata_sil24 driver. Then I checked to see if it was loaded, and it looks like it is,

smolloy@linux:~> lsmod | grep -i sata_sil24
sata_sil24             28676  0 
libata                 90904  2 sata_sil24,sata_nv
scsi_mod              163760  6 st,sr_mod,sata_sil24,sg,libata,sd_mod

When I find the time, I'll try compiling a 2.6.19 kernel to see if it works.

I'll let you know how successful I am.

[bigtomrodney]

I didn't realise this thread was going on. I have two Western Digital 320GB drives, and I have yanked both of them for various reasons, and reattached without problems. I use the sil driver too, but I'm not sure if it's the sil24.

[smolloy]

I didn't realise this thread was going on. I have two Western Digital 320GB drives, and I have yanked both of them for various reasons, and reattached without problems. I use the sil driver too, but I'm not sure if it's the sil24.

What kernel are you using?

There might be something else going on with my system that is preventing it from hotplugging. Would hotplug events be registered in the dmesg output?

[bigtomrodney]

They should be visible as events through dmesg. When I was doing this I would have been using SUSE 10.0 and Mandriva 2005 LE.

I'm using SUSE 10.2 now, and haven't done it recently.