On Aug 21, 2010, at 2:14 PM, Bill Sommerfeld <bill.sommerf...@oracle.com> wrote:
> On 08/21/10 10:14, Ross Walker wrote: >> I am trying to figure out the best way to provide both performance and >> resiliency given the Equallogic provides the redundancy. > > (I have no specific experience with Equallogic; the following is just generic > advice) > > Every bit stored in zfs is checksummed at the block level; zfs will not use > data or metadata if the checksum doesn't match. I understand that much and is the reason I picked ZFS for persistent data storage. > zfs relies on redundancy (storing multiple copies) to provide resilience; if > it can't independently read the multiple copies and pick the one it likes, it > can't recover from bitrot or failure of the underlying storage. Can't auto-recover, but will report the failure so it can be restored from backup, but since the vmdk files are too big to backup... > if you want resilience, zfs must be responsible for redundancy. Must have, not necessarily have full control. > You imply having multiple storage servers. The simplest thing to do is > export one large LUN from each of two different storage servers, and have ZFS > mirror them. Well... You need to know that the multiple storage servers are acting as a single pool with tiered storage levels (SAS 15K in RAID10 and SATA in RAID6) and luns are auto-tiered across these based on demand performance, so a pool of mirrors won't really provide any more performance then a raidz (same physical RAID) and raidz will only "waste" 33% as oppose to 50%. > While this reduces the available space, depending on your workload, you can > make some of it back by enabling compression. > > And, given sufficiently recent software, and sufficient memory and/or ssd for > l2arc, you can enable dedup. The host is a blade server with no room for SSDs, but if SSD investment is needed in the future I can add an SSD Equallogic box to the storage pool. > Of course, the effectiveness of both dedup and compression depends on your > workload. > >> Would I be better off forgoing resiliency for simplicity, putting all my >> faith into the Equallogic to handle data resiliency? > > IMHO, no; the resulting system will be significantly more brittle. Exactly how brittle I guess depends on the Equallogic system. -Ross _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
