LinuxQuestions.org
Review your favorite Linux distribution.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - General
User Name
Password
Linux - General This Linux forum is for general Linux questions and discussion.
If it is Linux Related and doesn't seem to fit in any other forum then this is the place.

Notices


Reply
  Search this Thread
Old 08-15-2006, 11:08 AM   #1
weshutchins
Member
 
Registered: Oct 2003
Location: Phoenix, AZ USA
Posts: 31

Rep: Reputation: 0
Disk (SCSI/SATA/ATA) Host Bus Adapter DMA


When a disk to disk transfer occurs and the disks reside on different host bus adapters (HBA) does the data get DMAed to from one HBA to the other HBA or does one HBA DMA data to ram while the other DMAs from ram? For performance the HBA to HBA DMA would be the fastest.
 
Old 08-16-2006, 05:50 AM   #2
timmeke
Senior Member
 
Registered: Nov 2005
Location: Belgium
Distribution: Red Hat, Fedora
Posts: 1,515

Rep: Reputation: 61
As far as my hardward knowledge goes, DMA is short for Direct Memory Access. It is used by devices like hard disks, to temporarily gain control over the system bus (normally, the CPU has control over the bus), so that they can access the memory directly for read/write operations.
In other words, DMA simply omits the CPU as "middle-man" in hard disk <-> memory transactions. The device will notify the CPU afterwards so that it can regain control over the bus.

In theory, the disk could use it's control over the bus to "contact" another device (ie another hard disk), but
this seems unlikely, for many reasons: ie different hard disk speeds, different lengths of data bursts, disk caching, 2 disks with alternating control over the bus, etc).
 
Old 08-16-2006, 10:18 AM   #3
weshutchins
Member
 
Registered: Oct 2003
Location: Phoenix, AZ USA
Posts: 31

Original Poster
Rep: Reputation: 0
I'm guessing that a HBA can only DMA to system memory (ram) but that a smart OS could simultaneously setup a read from one HBA and a write to another HBA. It could be done in blocks of sectors (128?). The write would occur after the first block was read. So the transfer would be limited to the system speed unless the system speed was at least twice as fast as the slowest HBA/drive. Probably the slowest HBA/drive is the limiting factor.

thanx for the reply

Last edited by weshutchins; 08-16-2006 at 10:20 AM.
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
QLogic Host Bus Adapter Driver @nthony Linux - Hardware 0 06-19-2006 03:44 PM
error after make all for host bus adapter driver temm Linux - Hardware 5 10-28-2005 09:10 AM
help how to install driver of Fibre channel Host Bus Adapter(HBA) on Slackware 10 zhouj Slackware 1 12-06-2004 08:37 AM
Hard Disk and DMA Problems with 160GB ATA/100 HDD Shadowman2oo3 Linux - Hardware 4 08-10-2004 09:19 PM
Tekram DC 315U SCSI Host Adapter Joe47 Linux - Newbie 0 06-23-2003 01:03 AM

LinuxQuestions.org > Forums > Linux Forums > Linux - General

All times are GMT -5. The time now is 01:37 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration