File as generic block-device?

File as generic block-device?

[Simen Thoresen]

Hi all,

I have a project where I require to treat a file as a block-device 
(specifically, I want a file on an ext3 fs to act as one of the 
raid-members in a md-based stripe-set. I know that I can make a 
/filesystem/ on a file because both mkfs and mount (with -o loop) will 
accept a file as a block-device, but I have found no such function for 
mdadm, and am thus asking for a kernel-internal way to re-plug a file 
into the block-device layer.

Is this possible?

My current platform i CentOS5, a RHEL5 rebuild (modified 2.6.18-kernel).

-S
-- 
Simen Thoresen - Dolphin ICS Systems Administrator

Re: File as generic block-device?

[Geert Uytterhoeven]

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On Wed, 22 Oct 2008, Simen Thoresen wrote:
> I have a project where I require to treat a file as a block-device
> (specifically, I want a file on an ext3 fs to act as one of the raid-members
> in a md-based stripe-set. I know that I can make a /filesystem/ on a file
> because both mkfs and mount (with -o loop) will accept a file as a
> block-device, but I have found no such function for mdadm, and am thus asking
> for a kernel-internal way to re-plug a file into the block-device layer.
> 
> Is this possible?

Sure! You just have to create the loop device (/dev/loop*) yourself using
losetup(8). `mount -o loop' does it itself behind your back.

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
Fax:      +32 (0)2 700 8622
E-mail:   Geert.Uytterhoeven@sonycom.com
Internet: http://www.sony-europe.com/

A division of Sony Europe (Belgium) N.V.
VAT BE 0413.825.160 · RPR Brussels
Fortis · BIC GEBABEBB · IBAN BE41293037680010

Re: File as generic block-device?

[martin f krafft]

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also sprach Simen Thoresen <simentt@dolphinics.no> [2008.10.22.1456 +0200]:
> accept a file as a block-device, but I have found no such function
> for  mdadm, and am thus asking for a kernel-internal way to
> re-plug a file  into the block-device layer.

I suggest you search the web first.
http://en.wikipedia.org/wiki/Loopback_disk_device

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
"you don't sew with a fork, so i see no reason
 to eat with knitting needles."
                               -- miss piggy, on eating chinese food
 
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Re: File as generic block-device?

[Simen Thoresen]

Geert Uytterhoeven wrote:
> On Wed, 22 Oct 2008, Simen Thoresen wrote:
>> I have a project where I require to treat a file as a block-device
>> (specifically, I want a file on an ext3 fs to act as one of the raid-members
>> in a md-based stripe-set. I know that I can make a /filesystem/ on a file
>> because both mkfs and mount (with -o loop) will accept a file as a
>> block-device, but I have found no such function for mdadm, and am thus asking
>> for a kernel-internal way to re-plug a file into the block-device layer.
>>
>> Is this possible?
> 
> Sure! You just have to create the loop device (/dev/loop*) yourself using
> losetup(8). `mount -o loop' does it itself behind your back.

Ah! Perfect, thank you.

-S

> With kind regards,
> 
> Geert Uytterhoeven
> Software Architect
> 
> Sony Techsoft Centre Europe
> The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium
> 
> Phone:    +32 (0)2 700 8453
> Fax:      +32 (0)2 700 8622
> E-mail:   Geert.Uytterhoeven@sonycom.com
> Internet: http://www.sony-europe.com/
> 
> A division of Sony Europe (Belgium) N.V.
> VAT BE 0413.825.160 · RPR Brussels
> Fortis · BIC GEBABEBB · IBAN BE41293037680010


-- 
Simen Thoresen - Dolphin ICS Systems Administrator

Re: File as generic block-device?

[Simen Thoresen]

martin f krafft wrote:
> also sprach Simen Thoresen <simentt@dolphinics.no> [2008.10.22.1456 +0200]:
>> accept a file as a block-device, but I have found no such function
>> for  mdadm, and am thus asking for a kernel-internal way to
>> re-plug a file  into the block-device layer.
> 
> I suggest you search the web first.
> http://en.wikipedia.org/wiki/Loopback_disk_device

Thank you - I missed googling for the absolutely obvious.

Sigh.

-S



-- 
Simen Thoresen - Dolphin ICS Systems Administrator