Losing space on a RAID 5 array

Losing space on a RAID 5 array

Post by Justi » Sat, 15 Dec 2001 03:23:10



We are using an Adaptec ATA-2400a RAID card on 4.4 Stable.  We have 4
76.8GB disks in a RAID 5 so the size should be 3x76.8 GB disks= 230.4?
(not counting the 4th drive we lose due to the raid 5)

yet the total size of the actual array is only 208GB?

And were losing another 16GB somewhere, since there is no data on the
drives:

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/da2s1e   208G   1.0K   192G     0%    /data0

Any idea why were losing that much space?

Thanks in advance.

 
 
 

Losing space on a RAID 5 array

Post by Rob MacGrego » Sat, 15 Dec 2001 03:28:00



> We are using an Adaptec ATA-2400a RAID card on 4.4 Stable.  We have 4
> 76.8GB disks in a RAID 5 so the size should be 3x76.8 GB disks= 230.4?
> (not counting the 4th drive we lose due to the raid 5)

> yet the total size of the actual array is only 208GB?

> And were losing another 16GB somewhere, since there is no data on the
> drives:

> Filesystem      Size   Used  Avail Capacity  Mounted on
> /dev/da2s1e   208G   1.0K   192G     0%    /data0

> Any idea why were losing that much space?

Disks are sold with 1 MB = 1000 KB, 1 GB = 1000 MB...

So, that 76.8 GB disk is actually 71.5 GB, so 3 are about 214 GB.  You'll
lose some to file system overhead too...

--
  Rob MacGregor (MCSE) [PGP key ID 0x1F5239DD]
      The light at the end of the tunnel is an oncoming dragon.

Question intelligently:
http://www.tuxedo.org/~esr/faqs/smart-questions.html

 
 
 

Losing space on a RAID 5 array

Post by Marcus Edval » Fri, 14 Dec 2001 03:37:54



Quote:> We are using an Adaptec ATA-2400a RAID card on 4.4 Stable.  We have 4
> 76.8GB disks in a RAID 5 so the size should be 3x76.8 GB disks= 230.4?
> (not counting the 4th drive we lose due to the raid 5)

> yet the total size of the actual array is only 208GB?

> And were losing another 16GB somewhere, since there is no data on the
> drives:

> Filesystem      Size   Used  Avail Capacity  Mounted on
> /dev/da2s1e   208G   1.0K   192G     0%    /data0

> Any idea why were losing that much space?

> Thanks in advance.

man newfs, look for -m
 
 
 

1. Not wasting space on a RAID array?

I have a RAID A1000 module that I am setting up.

Suppose I create one LUN of, say, 50GB on the module.

When I use the 'format' command to create partitions on the LUN, s2 sees
only 48GB or so.

Is there a way I can get to use my full 50GB LUN and 'newfs' a 50GB
filesystem?

Also, how does 'format' calculate the 48GB from 50GB? Whats the formula?

Thanks for any help

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