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Converting single non-raid to raid1



Excellent points that I did not consider before. After reading this post
and Dan's post regarding the boot partition, I think the advantage of
using RAD1 on the boot partition is that both partitions would
automatically be in sync, but if the drive with the updated boot block
fails, one could also boot from a DVD and rebuild the MBR. Asfar as SWAP
is concerned I have plenty of memory so SWAP would never really come
into play. One decision would be to make swap an LVM (as I currently
have it) or essentially to have 3 RAID volumes:
md0 - /boot to keep it near the beginning of the drive.
md1 - swap - Does not really matter too much since swap should not come
into play very often.
md2 - LVM volume group.




On 02/17/2010 11:29 AM, Mark J Dulcey wrote:
> On 2/17/2010 11:06 AM, Jerry Feldman wrote:
>
>  =20
>> Does the new physical drive need to be the same geometry as the older
>> drive. Let's say I have a Seagate 1TB, and buy a new WD 1TB drive, wil=
l
>> that cause a problem as long as the raid partition on both are the sam=
e
>> size.
>>    =20
> No special requirements for geometry. The only constraint is that the=20
> RAID can only be as large as the smaller of the two drives -- drives=20
> from different manufacturers and even different manufacturing runs vary=
=20
> slightly in size.
>
> There is an argument in favor of using non-identical drives. Drives fro=
m=20
> the same manufacturing run tend to have correlated failures (that is,=20
> they're more likely than normal to fail at about the same time -- that'=
s=20
> one reason that RAID 5 setups have been far less reliable in the real=20
> world than statistical analysis predicted), so it's better to make your=
=20
> RAID 1 out of drives from different manufacturers or at least different=
=20
> manufacturing lots.
>
>  =20
>> Secondly, is there any advantage or disadvantage to allocating the boo=
t
>> partition as a raid1. I think in a prior discussion, there was an
>> overwhelming opinion that swap should be on the raid1.
>>    =20
> Using RAID1 for the boot partition gives you a built-in backup, though =

> GRUB won't take advantage of it automatically (it loads the OS from the=
=20
> boot partition as an ordinary non-RAID ext3 or whatever) so you might=20
> have to manually reconfigure your boot setup to recover from a drive=20
> failure.
>
> Swap on RAID1 gives you higher read performance (because the reads can =

> be divided), slightly lower write performance (because the data has to =

> be written to both drives, and there is more CPU overhead), and data=20
> integrity. All in all a good deal. But with RAM as cheap as it is=20
> nowadays, why is your system swapping?
>  =20

--=20
Jerry Feldman <gaf-mNDKBlG2WHs at public.gmane.org>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846








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