Re: btrfs RAID with enterprise SATA or SAS drives

[Martin Steigerwald <ms@teamix.de>]

Am Mittwoch, 9. Mai 2012, 22:01:49 schrieb Daniel Pocock:
> There is various information about
> - enterprise-class drives (either SAS or just enterprise SATA)
> - the SCSI/SAS protocols themselves vs SATA
> having more advanced features (e.g. for dealing with error conditions)
> than the average block device
> 
> For example, Adaptec recommends that such drives will work better with
> their hardware RAID cards:
[…]
> - for someone using SAS or enterprise SATA drives with Linux, I
> understand btrfs gives the extra benefit of checksums, are there any
> other specific benefits over using mdadm or dmraid?

I think I can answer this one.

Most important advantage I think is BTRFS is aware of which blocks of the 
RAID are in use and need to be synced:

- Instant initialization of RAID regardless of size (unless at some 
capacity mkfs.btrfs needs more time)

- Rebuild after disk failure or disk replace will only copy *used* blocks


Scrubbing can repair from good disk if RAID with redundancy, but SoftRAID 
should be able to do this as well. But also for scrubbing: BTRFS only 
check and repairs used blocks.


Another advantage in the future – not yet possible AFAIK:

- Different RAID levels on same filesystem yet different subvolumes, more 
flexibility as subvolumes are dynamically allocated, instead of statically 
sized

Ciao,
Martin

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Martin Steigerwald
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