On 05/01/2010 16:00, Roch wrote:
That said, I truly am for a evolution for random read workloads. Raid-Z on 4K sectors is quite appealing. It means that small objects become nearly mirrored with good random read performance while large objects are stored efficiently.
Have you got any benchmarks available (comparing 512B to 4K to classical RAID-5)?
The problem is that while RAID-Z is really good for some workloads it is really bad for others. Sometimes having L2ARC might effectively mitigate the problem but for some workloads it won't (due to the huge size of a working set). In such environments RAID-Z2 offers much worse performance then similarly configured NetApp (RAID-DP, same number of disk drives). If ZFS would provide another RAID-5/RAID-6 like protection but with different characteristics so writing to a pool would be slower but reading from it would be much faster (comparable to RAID-DP) some customers would be very happy. Then maybe a new kind of cache device would be needed to buffer writes to NV storage to make writes faster (like "HW" arrays have been doing for years).
A possible *workaround* is to use SVM to set-up RAID-5 and create a zfs pool on top of it.
How does SVM handle R5 write hole? IIRC SVM doesn't offer RAID-6. -- Robert Milkowski http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
