Questions[opensolaris](server)

I'm using Nexentastor on a secondary storage server running on an HP ProLiant DL180 G6 with 12 Midline (7200 RPM) SAS drives. The system has an E5620 CPU and 8GB RAM. There is no ZIL or L2ARC device.

Last week, I created a 750GB sparse zvol with dedup and compression enabled to share via iSCSI to a VMWare ESX host. I then created a Windows 2008 file server image and copied ~300GB of user data to the VM. Once happy with the system, I moved the virtual machine to an NFS store on the same pool.

Once up and running with my VMs on the NFS datastore, I decided to remove the original 750GB zvol. Doing so stalled the system. Access to the Nexenta web interface and NMC halted. I was eventually able to get to a raw shell. Most OS operations were fine, but the system was hanging on the zfs destroy -r vol1/filesystem command. Ugly. I found the following two OpenSolaris bugzilla entries and now understand that the machine will be bricked for an unknown period of time. It's been 14 hours, so I need a plan to be able to regain access to the server.

http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6924390

and

http://bugs.opensolaris.org/bugdatabase/view_bug.do;jsessionid=593704962bcbe0743d82aa339988?bug_id=6924824

In the future, I'll probably take the advice given in one of the buzilla workarounds:

Workaround
    Do not use dedupe, and do not attempt to destroy zvols that had dedupe enabled.

Update: I had to force the system to power off. Upon reboot, the system stalls at Importing zfs filesystems. It's been that way for 2 hours now.

Currently we use an iSCSI SAN as storage for several VMware ESXi servers. I am investigating the use of an NFS target on a Linux server for additional virtual machines. I am also open to the idea of using an alternative operating system (like OpenSolaris) if it will provide significant advantages.

What Linux-based filesystem favours very large contiguous files (like VMware's disk images)? Alternatively, how have people found ZFS on OpenSolaris for this kind of workload?

(This question was originally asked on SuperUser; feel free to migrate answers here if you know how).

I've been working with OpenSolaris and ZFS for 6 months, primarily on a Sun Fire x4540 and standard Dell and HP hardware. One downside to standard Perc and HP Smart Array controllers is that they do not have a true "passthrough" JBOD mode to present individual disks to ZFS.

One can configure multiple RAID 0 arrays and get them working in ZFS, but it impacts hotswap capabilities (thus requiring a reboot upon disk failure/replacement). I'm curious as to what SAS/SATA controllers are recommended for home-brewed ZFS storage solutions. In addition, what effect does battery-backed write cache (BBWC) have in ZFS storage?

I'm planning on building a file server using OpenSolaris and ZFS that will provide two primary services - be an iSCSI target for XenServer virtual machines & be a general home file server. The hardware I'm looking at includes 2x 4-port SATA controllers, 2x small boot drives (one on each controller), and 4x big drives for storage. This allows one free port per controller for upgrading the array down the road.

Where I'm a little confused is how to setup the storage drives. For performance, mirroring appears to be king. I'm having a hard time seeing what the benefit would be of using RAIDZ over mirroring would be. With this setup I can see two options - two mirrored pools in one stripe, or RAIDZ2. Both should protect against 2 drive failures, and/or one controller failure...the only benefit of RAIDZ2 would be that any 2 drives could fail. The storage should be 50% of capacity in both cases, but the first should have much better performance, right?

The other thing I'm trying to wrap my mind around is the benefit of mirrored arrays with more than two devices. For data integrity what, if any, would be the benefit of a RAIDZ over a three-way mirror? Since ZFS maintains file integrity what does RAIDZ bring to the table...doesn't ZFS's integrity checks negate the value of RAIDZ's parity?

I'm planning on installing OpenSolaris on my home server (right now it has Linux) and I would like to know how to prepare for upgrading the server to have larger hard drives in the future. Now the server has 4x 400GB SATA drives and I would install OpenSolaris with ZFS RAID-Z on them. Some time later this or next year I'm going to upgrade the drives to maybe 4x 1TB SATA drives.

How can I do the upgrading and increasing of the partition size with ZFS? Is it a simple and painless operation (e.g. replace one drive at a time and ZFS will automatically resize itself to use the full space), or are some special steps required? Can it be done without shutting down the system?