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Having trouble installing a piece of hardware? Want to know if that peripheral is compatible with Linux?

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Old 10-23-2008, 12:44 PM   #1
abefroman
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Sata drive being recogniced as IDE???


Sata drive being recogniced as IDE???

When I do a df I get
/dev/hda for my Sata drive, I thought hd is an IDE drive, shouldn't that be sd?
 
Old 10-23-2008, 12:46 PM   #2
CRC123
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Quote:
Originally Posted by abefroman View Post
Sata drive being recogniced as IDE???

When I do a df I get
/dev/hda for my Sata drive, I thought hd is an IDE drive, shouldn't that be sd?
I'm not certain, but perhaps your BIOS has an 'IDE emulation' mode for sata and it presents the sata drive as an IDE drive to the OS. To get it to show up as SATA, there is normally an 'AHCI' or 'RAID' option that can be used instead. However, be careful; your initial ram disk may not have the sata modules in it since you installed using 'IDE emulation'.
 
Old 10-23-2008, 07:01 PM   #3
onebuck
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Hi,

You should make sure that your BIOS is setup to 'AHCI'.

What distribution & kernel?

At boot you should be able to pass the kernel parameter 'hda=noprobe' if hda is your device, change to suit.
 
Old 10-23-2008, 11:47 PM   #4
jay73
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CentOS has an older kernel, possibly one that predates the switch to libata so it would make sense that the drives appear as hd rather than sd.
 
Old 10-24-2008, 12:53 AM   #5
lazlow
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Jay

Even in the older kernels (at least back to FC4) sata drives are sdX (unless bios is set otherwise).
 
Old 10-24-2008, 12:55 AM   #6
onebuck
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Hi,

Quote:
Originally Posted by jay73 View Post
CentOS has an older kernel, possibly one that predates the switch to libata so it would make sense that the drives appear as hd rather than sd.
I think CentOS started with 5.0 (2.6 kernel) using the libATA. That was back in 2006 or early 2007.

I think that libata stable was available around 2.6.17 (I think that was back in 2006). I would have to do some research to be sure. Most modern kernels for most distributions support the 'libata' now.

So I think the suggestion to pass the parameter 'hda=noprobe' was a valid assumption that libata was being used.
 
Old 10-27-2008, 12:51 AM   #7
abefroman
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Quote:
Originally Posted by CRC123 View Post
I'm not certain, but perhaps your BIOS has an 'IDE emulation' mode for sata and it presents the sata drive as an IDE drive to the OS. To get it to show up as SATA, there is normally an 'AHCI' or 'RAID' option that can be used instead. However, be careful; your initial ram disk may not have the sata modules in it since you installed using 'IDE emulation'.
Thanks you were exactly right.
 
Old 10-27-2008, 12:53 AM   #8
abefroman
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You should make sure that your BIOS is setup to 'AHCI'.
>>Yes, thats is what helped, thanks!

What distribution & kernel?
>>Centos, latest kernel

At boot you should be able to pass the kernel parameter 'hda=noprobe' if hda is your device, change to suit.
>>I tried that before, it helped, but only slightly
 
Old 10-27-2008, 01:38 AM   #9
Electro
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It is ok that your BIOS is telling the on-board SATA controller to be as IDE. Features like hot swap will not work, but your hardware will be more compatible.

Just to note AHCI is slow and has poor latency. Maybe in the few years AHCI compatible hardware will improve.
 
Old 10-27-2008, 02:04 AM   #10
jay73
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Isn't that the whole point of AHCI, Electro? As I understand it, the NCQ feature of AHCI calculates the most efficient way of accessing/writing data so it will always have lower latency (because of the overhead of the calculation). This would make it slower on home computers but potentially faster on busy servers that are doing reads and writes all the time as it reduces head movement. Rather than accessing a sector near the middle of the drive (B), then one at the end (C) and then one at the start (A) , AHCI would queue these requests and re-order them as A-B-C.

Last edited by jay73; 10-27-2008 at 02:07 AM.
 
Old 10-28-2008, 02:06 AM   #11
Electro
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NCQ is just a fancy word for task queue feature in SCSI. NCQ has nothing to do with AHCI. From the specification sheet for AHCI, it relies on software to tell the controller what to do. In simpler terms, AHCI is high level of talking to the storage controller. Let us just say that AHCI is a last resort option if Linux does not support the controller at low level.
 
  


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