What size and type of hard disk for my hw raid controller?

[edgars70]

Hi,

I've got a hardware raid controller (dell perc 5/i) for my nas. My homebrew nas only has 4 sata ports on it and I thought this card would be a good way to increase my port count and improve my raid 5 writes. I use my NAS as part of my backup strategy (I don't want to get into a raid is not backup discussion ;-).

Anyway, my plan was to buy 4 2TB disks and put them into Raid 5 until I read this why-raid-5-stops-working-in-2009 and
why-raid-6-stops-working-in-2019. I am thinking that I should probably buy 1TB disks to reduce the chance of a rebuild failure should one disk fail.

What are your opinions? Should I go Raid 5 with 1 or 2TB drives, or just stick to raid 1?

I'd also be happy to hear your opinion on which drives to use.

Thanks

[Jay]

Can you not do raid 10?

[shaithis]

Even if your OS does not support the newer larger partition sizes you can carve the raidset into volumes of 2TB or less using the RAID BIOS, each raid volume is presented to the OS as an individual drive.

[kingpotnoodle]

The articles are corrrect, with larger capacity drives RAID6 is much more likely to be more reliable.

A RAID 5 may fail to rebuild if another disk error occurs in the parity data during the rebuild. A RAID 6 stores 2 copies of the parity data, very unlikely that a piece of parity data will be hit by additional disk errors twice (unless you're array is proper f**!!d).

With 4 disks a RAID6 offers same capacity as a RAID 10, but the 6 will have worse performance because of the parity calculations. RAID 10 however could suffer from some of the same rebuild issues, if the other half of the mirror has any errors whilst degraded there is a data loss scenario but probably only in the damaged data sectors rather than total rebuild failure (not sure, never tried to run through that scenario).

RAID 6 is safest with large capacity drives. I assume from you're post you're aware how limited this 'safety' is ;-)

[peterb]

The articles are corrrect, with larger capacity drives RAID6 is much more likely to be more reliable.

A RAID 5 may fail to rebuild if another disk error occurs in the parity data during the rebuild. A RAID 6 stores 2 copies of the parity data, very unlikely that a piece of parity data will be hit by additional disk errors twice (unless you're array is proper f**!!d).

With 4 disks a RAID6 offers same capacity as a RAID 10, but the 6 will have worse performance because of the parity calculations. RAID 10 however could suffer from some of the same rebuild issues, if the other half of the mirror has any errors whilst degraded there is a data loss scenario but probably only in the damaged data sectors rather than total rebuild failure (not sure, never tried to run through that scenario).

RAID 6 is safest with large capacity drives. I assume from you're post you're aware how limited this 'safety' is ;-)

Well, the artcle is correct - to a point. The comments make interesting reading.

Firstly the Unrecoverable Error Rate is a mean value and a URE can ccur on a isk of any size at any time, and as ne commenter says, wil probably only resut in corruption of one file (and then the failing sector will be marked out of use, and a spare sector mapped in). And even if the array does go off line while t is rebulding, because of a URE, it doesn't mean that the data is lost. Putting the array back on line and restarting a rebuild may be successful, or the data can be recovered while further investigation is carried out.

Basically all the article says is that withh current drive sizes, and the current predicted URE, there is statistically a higher cahnce of rebuild failure in RAID5 when one drive has been replaced. If the RE value is changed, it changes the calculation, but that is a mean vale from (presumably)accelerated use tests, or modelling.

BUT - what the article does re-enforce is the fact that RAID is NOT substitute for having a proper backup regime. RAID is more about resiliance and server uptime - a fact many people forget.

[1stRaven]

BUT - what the article does re-enforce is the fact that RAID is NOT substitute for having a proper backup regime. RAID is more about resiliance and server uptime - a fact many people forget.

And performance...

Until SSD drives dropped in price, Raid was one of the only methods of increase disk performance past a certain point. Resilience and uptime took a dive possible depending on the raid type though.