RAID over Firewire

RAID over Firewire

[Richard Scobie]

Has anyone had any experience or comment regarding linux RAID over ieee1394?

As a budget backup solution, I am considering using a pair of 500GB 
drives, each connected to a firewire 400 port, configured as a linear 
array, to which the contents of an onboard array will be rsynced weekly.

In theory, throughput performance should not be an issue, but it would 
be great to hear from somone who has done this.

Regards,

Richard

Re: RAID over Firewire

[Gregory Seidman]

On Wed, Aug 23, 2006 at 11:35:26AM +1200, Richard Scobie wrote:
} Has anyone had any experience or comment regarding linux RAID over ieee1394?
} 
} As a budget backup solution, I am considering using a pair of 500GB 
} drives, each connected to a firewire 400 port, configured as a linear 
} array, to which the contents of an onboard array will be rsynced weekly.
} 
} In theory, throughput performance should not be an issue, but it would 
} be great to hear from somone who has done this.

My main concern has been redundancy rather than performance, but I have had
no issues with my setup: 2x250GB FW 400 drives running LVM on dm_crypt on 
RAID1. This is my home IMAP(S)/HTTP(S)/NFS/shell server. I've recently set
up the same thing for my mother. I'm really happy with it.

} Regards,
} Richard
--Greg

Re: RAID over Firewire

[Martin Schröder]

2006/8/23, Richard Scobie <richard@sauce.co.nz>:
> As a budget backup solution, I am considering using a pair of 500GB
> drives, each connected to a firewire 400 port, configured as a linear
> array, to which the contents of an onboard array will be rsynced weekly.

You can get 1TB+ RAID0 FW800 "drives". LaCie even sells FW RAIDs with
RAID 5 + Hotspare. :-)

Best
   Martin

Re: RAID over Firewire

[Richard Scobie]

Gordon Henderson wrote:

> While I haven't done this, I have a client who uses Firewire drives
> (Lacie) as a backup solution and they seem to "just work", and look like
> locally attached SCSI drives (Performance is quite good too!) I guess you
> won't be hot pluging/unplugging them, so those issues won't bite you, but
> I can't see a reason why a pair of them wouldn't be OK.

Thanks.

While I can see that hotunplugging without unmounting would be an issue,
what is the problem with hot plugging or unplugging otherwise?

Regards,

Richard

Re: RAID over Firewire

[Gordon Henderson]

On Thu, 24 Aug 2006, Richard Scobie wrote:

> Gordon Henderson wrote:
>
> > While I haven't done this, I have a client who uses Firewire drives
> > (Lacie) as a backup solution and they seem to "just work", and look like
> > locally attached SCSI drives (Performance is quite good too!) I guess you
> > won't be hot pluging/unplugging them, so those issues won't bite you, but
> > I can't see a reason why a pair of them wouldn't be OK.
>
> Thanks.
>
> While I can see that hotunplugging without unmounting would be an issue,
> what is the problem with hot plugging or unplugging otherwise?

Mostly dumb user issues - unplugging before unmounting, but I have seen
issues in older kernels where the
 echo "scsi remove-single-device 0 0 0 0" > /proc/scsi/scsi
rune has crashed the server.

Gordon

Re: RAID over Firewire

[Richard Scobie]

Dexter Filmore wrote:

> Of all modes I wouldn't use a linear setup for backups. One disk dies - all 
> data is lost.

> I'd go for an external raid5 solution, tho those tend to be slow and 
> expensive.
> 

Unfortunately "budget" is the overriding factor here. Unlike RAID 0, I
thought there may be a way of recovering data from undamaged disks in a
linear array, although I guess the file system used has some say in this.

I hope to mitgate the risk somewhat by regularly using smartd to do long
self tests on the disks.

Regards,

Richard

Re: RAID over Firewire

[Mike Hardy]

Richard Scobie wrote:
> Dexter Filmore wrote:
> 
>> Of all modes I wouldn't use a linear setup for backups. One disk dies
>> - all data is lost.
> 
>> I'd go for an external raid5 solution, tho those tend to be slow and
>> expensive.
>>
> 
> Unfortunately "budget" is the overriding factor here. Unlike RAID 0, I
> thought there may be a way of recovering data from undamaged disks in a
> linear array, although I guess the file system used has some say in this.
> 
> I hope to mitgate the risk somewhat by regularly using smartd to do long
> self tests on the disks.


Long self tests will just tell you that you lost a block before RAID or
the FS notices it, it's not going to stop the block (and your data) from
going away.

One more disk and you have raid 5 at least with the same storage
capacity. md will transparently (to the OS, you'll get a log message)
recover from single block errors in raid5.

I'm not sure SMART works over firewire anyway. That's a question.

http://smartmontools.sourceforge.net/:

"As for USB and FireWire (ieee1394) disks and tape drives, the news is
not good. They appear to Linux as SCSI devices but their implementations
do not usually support those SCSI commands needed by smartmontools."

Note that page is slightly out of date - they mention SMART for SATA is
supported through a patch to mainline, but it is in fact mainline now.

-Mike

Re: RAID over Firewire

[Richard Scobie]

Mike Hardy wrote:


> I'm not sure SMART works over firewire anyway. That's a question.
> 
> http://smartmontools.sourceforge.net/:
> 
> "As for USB and FireWire (ieee1394) disks and tape drives, the news is
> not good. They appear to Linux as SCSI devices but their implementations
> do not usually support those SCSI commands needed by smartmontools."

Thanks, that is a good point I will follow up.

Re: RAID over Firewire

[Francois Barre]

2006/8/23, Richard Scobie <richard@sauce.co.nz>:
> Has anyone had any experience or comment regarding linux RAID over ieee1394?
>
I've been successfully running a 4x250Gb Raid5 over ieee1394 with XFS on top.
The 4 drives are sharing the same ieee1394 bus, so the bandwidth is
awfull, because they have to share 20Mb/s.
It happens from time to time that one drive is temporary lost, so I
must re-add it and resync... (I would have liked to put a bitmap on
it, but I get an oops... I did not have time to give it a closer look
yet).

> As a budget backup solution, I am considering using a pair of 500GB
> drives, each connected to a firewire 400 port, configured as a linear
> array, to which the contents of an onboard array will be rsynced weekly.

I would really suggest you to study a 3-drive raid5 scenario, because
the risk of temporary loosing a disk is not neglectible... Regarding
to the cost of an extra disk.

That was my 2cents..

Re: RAID over Firewire

[Bill Davidsen]

Richard Scobie wrote:

> Has anyone had any experience or comment regarding linux RAID over 
> ieee1394?
>
> As a budget backup solution, I am considering using a pair of 500GB 
> drives, each connected to a firewire 400 port, configured as a linear 
> array, to which the contents of an onboard array will be rsynced weekly.
>
> In theory, throughput performance should not be an issue, but it would 
> be great to hear from somone who has done this.

It should work, but I don't like it... it leaves you with a lot of 
exposure between backups.

Unless your data change a lot, you might consider a good incremental 
dump program to DVD or similar.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: RAID over Firewire

[Richard Scobie]

Bill Davidsen wrote:

> 
> It should work, but I don't like it... it leaves you with a lot of 
> exposure between backups.
> 
> Unless your data change a lot, you might consider a good incremental 
> dump program to DVD or similar.

Thanks. I have abandoned this option for various reasons, including 
people randomly unplugging the drives.

Rsync to another machine is the current plan.

Regards,

Richard

Re: RAID over Firewire

[Bill Davidsen]

Richard Scobie wrote:

> Bill Davidsen wrote:
>
>>
>> It should work, but I don't like it... it leaves you with a lot of 
>> exposure between backups.
>>
>> Unless your data change a lot, you might consider a good incremental 
>> dump program to DVD or similar.
>
>
> Thanks. I have abandoned this option for various reasons, including 
> people randomly unplugging the drives.
>
> Rsync to another machine is the current plan. 

At one time I was evaluating doing RAID1 to an NBD on another machine, 
using write-mostly to make it a one way process. I had to redeplot the 
hardware before I reached a conclusion, and it was with an older kernel, 
so I simply throw it out for discussion.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979