FC3 + raw devices

Rick Stevens rstevens at vitalstream.com
Mon May 9 22:51:28 UTC 2005


T. Horsnell wrote:
>>T. Horsnell wrote:
>>
>>>What's the situation with 'raw' and FC3?
>>>I want to get raw access to disks for test
>>>purposes but 'man raw' and 'whereis raw'
>>>show nothing.
>>
>>Same as for the rest of Linux: you can access a raw partition as
>>/dev/hdXY or /dev/sdXY (depending on technology), where X is a letter
>>and Y a number. So the first partition of your first IDE disk is
>>/dev/hda1.
>>
>>To refer to the whole disk, use /dev/hdX or /dev/sdX.
>>
>>Please note: get this wrong and you could delete your whole system. Be
>>careful. Use backups or a separate test system.
>>
>>Now the real question: what exactly are you trying to do, and why?
>>If you just want to see how fast your hard disk goes, try
>>hdparm -t /dev/hda
>>(or whatever).
> 
> 
> Hi James,
> 
> Maybe I should have said direct I/O instead of raw. I discovered
> the O_DIRECT option to open(2) over the weekend and have been busy
> trying to use it.
> What I want to do (and what I have been doing on my Alpha system)
> is to thrash any new disk I plug in to my SCSI bus, before putting
> it to general use. I do this using a long test (at least 48 hours)
> of write/read/verify, of records full of random data, of random length,
> to random positions on the disk. I want to avoid the cache (which doesnt
> happen if I use /dev/sd?) hence the 'raw' requirement.
> 
> And, joy of joys, I can now even use smartctl to monitor the disk
> health in the process. Its interesting to see the temperature
> rise as the disk starts to work hard...
> 
> I hadnt heard of hdparm - what a useful tool. It shows buffered
> read rates on my 140GB 10Krpm SCSI drives of 75MByte/sec, but on my new
> 300GB 10Krpm one, I only get 65MBytes/sec. They're all Seagate - and
> all < 3 months old. Strange that.

Have you tried iozone?  http://www.iozone.org
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
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