rmeden's questions

I have this zpool:

    bash-3.2# zpool status dpool
  pool: dpool
 state: ONLINE
 scan: none requested
 config:
        NAME                                     STATE     READ WRITE CKSUM
        dpool                                    ONLINE       0     0     0
          c3t600601604F021A009E1F867A3E24E211d0  ONLINE       0     0     0
          c3t600601604F021A00141D843A3F24E211d0  ONLINE       0     0     0

I would like to replace both of these disks with a single (larger disk). Can it be done? zpool attach allows me to replace one physical disk, but it won't allow me to replace both at once.

I have a Sun M4000 connected to an EMC CX4-120 array with a write-heavy database. Writes peak at around 1200 IO/s and 12MB/s.

According to EMC, I am saturating the write cache on the EMC array.

I think the simplest solution is to move the redo logs to a DRAM based SSD. This will reduce the load on the EMC array by half and apps won't be seeing log buffer waits. Yes, the DBWR may become a bottleneck, but the apps won't be waiting for it (like they do on redo commits!)

I currently cycle through about 4 4GB redo logs, so even 20GB or so of SSD would make a big difference. Since this is short-term storage and is constantly being overwritten, Flash based SSDs probably aren't a great idea.

The M4000 doesn't have any extra drive lots, so a PCI-E card would be perfect, I could go external or move boot volumes to the EMC and free up the local drives.

Sun sells a Flash Accelerator F20 PCIe card, but that seems to be a cache for some SATA disks, not a DRAM SSD solution. Details are sketchy, it doesn't list the M4000 as supported, and I'm tired of fighting Sun's phone tree looking for human help. :(

Do others agree that a DRAM SSD is the way to go? Any hardware recommendations?

UPDATE In addition to the info in a comment below, I tried various settings for "commit_write" and it didn't make a difference.