# question on hardware raid

## dialsc

hello,

i'm planing to extend my linux server with a hardware raid controler card since a while. meanwhile i decided that the Highpoint RocketRAID 3520: 8 Port SATA2 RAID-Kontroller could be a good choice. i intend to attach 8 1tb discs running in raid level 6. two question came up to me on this.

1. will the kernel support this hardware raid?

2. what kind of file system should i use in order to create a 6tb partition?

thank you very much for your help.

greez,

dialsc

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## alex.blackbit

yes, there is support for this controller in the linux kernel, it is SCSI_HPTIOP.

nobody can tell you which file system to use. there are several discussions available for reading here in this forum and out there in the internet.

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## dialsc

hi, thx a lot for the fast replay.

according the file system question. i didn't want anyone to give me a hint on what is the best. personaly i prefere ext3. i just wanted to know if someone could tell me which filesystem supports a 6tb partition on a 32 linux installation in generel. does ext3 support it?. furthermore do i have to compile anything else into the kernel in order to make such a big partition accessable?

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## NeddySeagoon

dialsc,

ext3 will be ok but the standard DOS Partition table will not. It has a hard 2T limit.

You need to use GPT and some tools that support it. GPT support is in the kernel under Advanced Partition Tables.

I think that gparted supports GPT partition tables.

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## dialsc

NeddySeagoon,

thx a lot for this info. i will have a look to it.

greez,

dialsc

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## gentoo-dev

Btw, if you don't like using GPT, use software raid.

If you can't afford a new raid card or the wait for a new card should it fail, use software raid. With a raid card, your system has a single point of failure: the raid card :)

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## Naib

 *gentoo-dev wrote:*   

> Btw, if you don't like using GPT, use software raid.
> 
> If you can't afford a new raid card or the wait for a new card should it fail, use software raid. With a raid card, your system has a single point of failure: the raid card 

 

a cpu is also a single point of failure

so is the psu

so is the SATA control chip

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## fangorn

for partition table gpt is an option. Then you will have to use parted (or the grapical versions) to create partitions. 

I chose to use lvm2 ontop of the hardware RAID device as I started with 5 1TB discs and added space later. This was necessary as I am using XFS and parted is not able of resizing partitions with XFS filesystem atm. 

If you are creating the RAID from the full 8 discs from the start this does not have to bother you, as you will not resize the partitions anyway. But it is another option.

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## fangorn

 *gentoo-dev wrote:*   

> Btw, if you don't like using GPT, use software raid.
> 
> If you can't afford a new raid card or the wait for a new card should it fail, use software raid. With a raid card, your system has a single point of failure: the raid card 

 

If you are that dependent on your data, build a second machine to mirror the data. And do backups to a third machine with minimum double the space.  :Wink: 

That's the way we do it.

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## dialsc

 *fangorn wrote:*   

> for partition table gpt is an option. Then you will have to use parted (or the grapical versions) to create partitions. 
> 
> I chose to use lvm2 ontop of the hardware RAID device as I started with 5 1TB discs and added space later. This was necessary as I am using XFS and parted is not able of resizing partitions with XFS filesystem atm. 
> 
> If you are creating the RAID from the full 8 discs from the start this does not have to bother you, as you will not resize the partitions anyway. But it is another option.

 

if i got you right, i could use lvm2 INSTEAD of gpt, couldn't i? this way i would create a logicalVolume with let's say 6tb and just initialize a e.g. ext3 file system on top of it, right?

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## HeissFuss

If you put the filesystem on the raw device (/dev/sdb for example) you don't need to use a partition table at all.  However, you can only have that one filesystem consuming the entire array.

You should only use lvm2 on top of the raid device if you have a need of multiple filesystems.  That would allow you to add drives later and expand your filesystems as you wish.  If you're only going to have one filesystem though, lvm2 is pointless.  If you have only one filesystem, it can easily be grown if the partition below it is increased.

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## dialsc

hi, i see. thank you very much. so i'm going to use lvm2 and create the partitions needed ontop of the raw raid device. but one question is still open to me.

if i use ext3 as the filesystem, what will be the maximum partition size it supports. i've found different information on that. one said 2tb others 16tb. what is correct? i intend to run the raid on a 32bit machine.

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## fangorn

As told before I use xfs, but I had a NAS once that had 4 TB (or what the harddisk manufacturers tell us to be 4 TB*  :Evil or Very Mad:  ) and claimed to use ext3. I never checked, though. It ran definately on a 32bit linux, because it was an old Celeron processor in there. 

*When they realized their legally risky position they made this Gigabyte/Gibibyte ISO standardisation BS in 1996

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## Cyker

I'm currently running software RAID5 on 4x1TB disks which are partitioned with linux RAID autodetect, and ext3 is running on top of that with a size of 3TB. (But being accessed with ext4-noextents driver  :Smile: )

I will be upgrading the drives to the new WD GP 2TB drives when they start to cost less than £Stupid (Wish I pre-bought them now; Started at £194 and then went straight to £250 on release!!  :Shocked: ), or maybe the enterprise versions if/when they come out.

Am a bit worried bout hitting this 2TB partition limit 'tho...

Could just go back to mounting the RAID on unpartitioned drives, but then I loose kernel auto-detection...

 *Naib wrote:*   

>  *gentoo-dev wrote:*   Btw, if you don't like using GPT, use software raid.
> 
> If you can't afford a new raid card or the wait for a new card should it fail, use software raid. With a raid card, your system has a single point of failure: the raid card  
> 
> a cpu is also a single point of failure
> ...

 

The difference is those parts are generically replaceable. If it ran for 5 years then broke, you could change the whole system, stick the drives in and it'd work.

It's trickier with hardware RAID, since not all cards speak the same 'language'. The more paranoid admins I know always buy RAID cards in batchs of at least two so that they don't have to worry about that issue so much.

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## NeddySeagoon

Cyker,

There is no 2TB partition limit on filesystems.

2TB is the maximum space that a DOS partition table can describe. Thats sectors of 515B and 32 bit counters. That gets you 0.5KiB*4GiB.

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## Cyker

 *NeddySeagoon wrote:*   

> Cyker,
> 
> There is no 2TB partition limit on filesystems.
> 
> 2TB is the maximum space that a DOS partition table can describe. Thats sectors of 515B and 32 bit counters. That gets you 0.5KiB*4GiB.

 

Uh... huh? O.o

<---- Is now confused

Clarification respectfully requested!

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## NeddySeagoon

Cyker,

Users with large raid arrays > 2Tb will find that they can only use the first 2Tb if they use an MSDOS partition table.

This is regardless of filesystem, its a limit of the MSDOS partition table using 32 bits to describe disk space in sectors.

MSDOS Partition Tables use a 32 bit address to the first block of a partition and a 32 bit count of the blocks in the partition, each block being 512B.

Users do not normally discover this until they have made their raid, formatted it with the filesystem of their choice and discovered that they only have 2Tb of space. Its not the filesystems fault, its the underlying partition description.

When you move to GPT, (or another partition table structure that uses more than 32 bits) you can describe more space and the 2Tb limit vanishes for most filesystems.

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## Cyker

So... you are saying there *is* a 2TB partition-size limit, excepting if you use a partition system other than the standard MBR partition type, but, there is no 2TB filesystem limit (I knew that already 'tho; The filesystem size limit depends on what filesystem is used after all!)

I assume cfdisk uses MS DOS partition tables...?

I don't think this will affect me until we get >2TB drives as my RAID array's md0 is already >2TB and works fine, and it sounds like I can get around it anyway by just not using a partition table for the array elements, and going direct to metal as it were  :Smile: 

Don't know much about GPT other than nothing in the PC world except WinXP 64-bit and higher can access them (I'm not even 100% sure you can boot from them!). IIRC there was an option for EFI GPT in the kernel under Advanced Partition types, but unless cfdisk supports them I wouldn't even know how to make one!

My curiosity has been piqued now... wonder if there's anything in the man pages...

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## gentoo-dev

GPT works fine. Last time I tried it, I had to use lilo though.

This only affects you if you use hardware raid because your computer only sees one big disk attached to one controller.

If you use software raid provided by the kernel, your computer sees partitions <2TB which are assembled into /dev/mdX device(s) which in turn can be formatted.

BTW, I find it easier to number the md devices after the partitions they are built upon, /dev/sd*X make up /dev/mdX

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