get the size of a special device (drive)

exodist has asked for the wisdom of the Perl Monks concerning the following question:

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Re: get the size of a special device (drive) by blazar (Canon) on May 30, 2007 at 21:18 UTC
I need my script to get the size (Preferably in bytes) of a hard drive, I tried this: my $Size = (-s "/dev/sda4"); but it always sets $Size to 0. Since this seems very OS-specific it may be sensible to use OS-specific tools. Anyway a module like Sys::Filesystem seems like a good start. I found it with a few seconds' CPAN search for Linux device. Other searches may return more appropriate results for you.	[reply]
Re^2: get the size of a special device (drive) by exodist (Monk) on May 30, 2007 at 21:26 UTC
Unfortunately what I am writing is a filesystem... But I went browsing through /proc and found /proc/partitions, when I cat that it shows partitions and sizes in blocks (1024 bytes each I believe) Is this standard and reliable from linux system to linux system?	[reply]
Re^3: get the size of a special device (drive) by blazar (Canon) on May 30, 2007 at 21:39 UTC
Unfortunately what I am writing is a filesystem... But I went browsing through /proc and found /proc/partitions, when I cat that it shows partitions and sizes in blocks (1024 bytes each I believe) Is this standard and reliable from linux system to linux system? I think something changed between 2.4 and 2.6, but I wouldn't take my own word as the ultimate Truth™ as I'm far from being an expert...	[reply]
Re: get the size of a special device (drive) by Joost (Canon) on May 30, 2007 at 21:21 UTC
How much OS-independence do you need? Since you're probably on linux, parsing the output of `df` or `df -h` would be very easy. Maybe look at /sys/block/drivename/size I don't think this can be solved completely OS-independently, but I'd be interested in something that worked better on all/most POSIX systems "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l] [select]
Re^2: get the size of a special device (drive) by exodist (Monk) on May 30, 2007 at 21:35 UTC
/sys/block/drivename/size is useful, it looks liek it uses 512k block size?	[reply]
Re^3: get the size of a special device (drive) by Joost (Canon) on May 30, 2007 at 22:28 UTC
I have no idea. It looked interesting, but I can't seem to find any real info on what the numbers in /sys/block//size mean at all. Personally, I'd go with `du -h` or `du -B 1` (for bytes) "What should it profit a man, if he should win a flame war, yet lose his cool?"*	[reply] [d/l] [select]
Re^4: get the size of a special device (drive) by blazar (Canon) on May 30, 2007 at 22:35 UTC
Re^5: get the size of a special device (drive) by Joost (Canon) on May 30, 2007 at 22:41 UTC
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Re^4: get the size of a special device (drive) by exodist (Monk) on May 31, 2007 at 00:18 UTC
Re: get the size of a special device (drive) by almut (Canon) on May 31, 2007 at 00:07 UTC
You could also parse the output of good ol' `fdisk` — e.g. `fdisk -l -u /dev/hda` (`-u` to display the info in units of sectors (the size of which it'll tell you, too)). Problem might be (depending on context) that it'll need to be run as root...	[reply] [d/l] [select]
Re: get the size of a special device (drive) by BrowserUk (Patriarch) on May 31, 2007 at 00:16 UTC
If all else fails, you could try seeking to the end of the 'file' using the end-relative seek mode: `open DEV, '<+:raw', '/dev/sda4' or die ... my $size = sysseek DEV, 0, 2;` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re: get the size of a special device (drive) by Util (Priest) on May 31, 2007 at 03:20 UTC
I don't have SCSI (sdX) drives on my system, but my IDE drive sizes are easy to determine. `$ cat /proc/ide/ide0/hda/capacity 78165360 $ cat /proc/ide/ide0/hdb/capacity 40718160 $ cat /proc/ide/ide1/hdd/capacity 241254720` [download] Trimmed output from `cfdisk` Disk Drive: /dev/hda Size: 40020664320 bytes, 40.0 GB Disk Drive: /dev/hdb Size: 20847697920 bytes, 20.8 GB Disk Drive: /dev/hdd Size: 123522416640 bytes, 123.5 GB [download] The /proc/ide/ideX/hdX/capacity size is in 512 byte blocks, and matches exactly (after multiplying by 512) with the size reported by `cfdisk`. Hopefully, there are analogous /proc/scsi//capacity files. Update:* the `capacity` files I describe above exactly match the `/sys/block/drivename/size` files that Joost mentioned. The `size` files are easier to navigate to. I can confirm that the units are exact 512 byte blocks.	[reply] [d/l] [select]
Re^2: get the size of a special device (drive) by exodist (Monk) on May 31, 2007 at 15:28 UTC
Thank you, using /sys/block/DriveName/size is my plan now. Since it has been confirmed it uses b12byte block size both for me and for others here I am going to trust it until I find reasons I shouldn't.	[reply]