[Alex Gerulaitis]

[Vadim Carter] “There is no need to wait for ZFS RAID Set to restripe. There is no reformatting involved. There is no risk to the data. It just works. Like magic.”

I could see how “no reformatting” works (legacy RAID expansions also don’t require reformatting) but no re-striping? Say, you added another eight drives to an existing set of eight in RAID-Z – how would the performance (transfer rates) of existing files improve w/o re-striping?

[Alex Gerulaitis]

It should theoretically work.

One issue to watch out for, is that some eSATA RAID boxes require port-replicated (aka port-multiplier) eSATA. If yours does, you’d want to ensure that device supports it.

[Alex Gerulaitis]

Thanks Abraham!

Would it possible to also move RAID level reliability thread to this new forum?

[Alex Gerulaitis]

Thanks for tuning in Bob,

Yes, iMacs with ATTO ThunderLink NT 1102 (the fans on which the client says are quite loud). NetGear XS708E switch. ATTO FFRM-NT12-000 on the xServe.

Jumbo frames are enabled all around except the switch – couldn’t figure out where to set them there.

Will check into tuning files.

Thanks again.

[Alex Gerulaitis]

[Stephen Pickering] “What’s the reason RAID 5 is less safe?”

Chances of drive failure or corrupted data during rebuild are higher than with RAID1, and in some cases (16TB RAID5 sets with desktop drives) are high enough so that people don’t recommend them unless the user understands the risk.

[Alex Gerulaitis]

[Eric Hansen] “Alex, you definitely trump me here, and i don’t want to hijack the thread. from what I understand, FC can failover because OS X can understand multi-pathing over FC”

I am a n00b in FC or Ethernet failover, all I did was a little reading and a couple of training sessions on a high-end iSCSI based SAN. So this is a very useful discussion for me.

No worries about thread hi-jacking – with Vadim’s help, RAID6 emerged as the winner in terms of reliability. So the thread is more or less done with. Appreciate your concern though – perhaps fork this into a new thread? Something like, “Ethernet vs. FC – which is more resilient?”

[Alex Gerulaitis]

[Eric Hansen] “the ability to expand a volume without reformatting is another awesome feature.”

I’ve done this with RAID5 and RAID6 volumes. Am I missing something? (Thought ZFS’s advantages were centered around resiliency, performance, integration with RAID-Z.)

[Eric Hansen] “this is the main thing I hate about ethernet-based SANs vs FC-based SANs”

Eric, would you elaborate on this?

My understanding was that layer 3 Ethernet switches could do auto-failover, something that’s not part of FC where failover is handled primarily on the driver or even ASIC level – but is not part of the “intelligence” of the protocol.

[Alex Gerulaitis]

Do you want to basically push one button and have a DVD recorded from an analog or firewire source?

Some software listed here does offer simplified DVD recording although you may still have to push maybe three buttons before you have a DVD.

Premiere Pro will do it (coupled with Encore), just it’ll more than a few buttons:
1. capture,
2. put captured material on the timeline,
3. Send to Encore
4. Make a DVD

… each step is a few buttons.

Alternately, you could use a device that does all that.

[Alex Gerulaitis]

[Stephen Pickering] “RAID1 would be best for my purpose, right?”

CR-H458 is a four-drive unit; do you plan to use just two drives for one mirror, or?…

With four drives, RAID5 might be better; it’s less reliable than RAID1 though.

[Stephen Pickering] “So if one drive fails I only lose the drive and not the data since it’s duplicated, right?”

Correct. Doesn’t protect against user error or file system corruption (most common causes of data loss) though, so backup is still paramount.

[Stephen Pickering] “If RAID1 is the best for my purpose, what’s the recovery process if one drive fails? Can I just pull out the good unit and copy the data to a new backup drive? Do I simply plug in a new drive for it to “rebuild” the array? “

The specs say “Auto-rebuild in RAID 5 mode” which I assume means, “no auto-rebuild in RAID 1 mode”. You’ll have to do it manually through the supplied RAID manager utility: replace the drive, start a rebuild.

HTH.

[Alex Gerulaitis]

[Vadim Carter] “Alex, here are a couple of papers that I had saved as a reference a while ago that seem to support your assertion that RAID 6 is more reliable than RAID 10”

Thanks Vadim. Couldn’t quite grasp the math on the first attempt, but I’ll try again, perhaps with a double espresso this time.

[Vadim Carter] “With 48x4TB drives, a rebuild of one drive can take days.”

I am hoping nobody does those really wide parity groups without understanding the implications. Personally, I’d do RAID60 on 48-wide group.

[Vadim Carter] “Same drive configurations in a RAID 10 arrangement only take a few hours to rebuild with a lot less I/O load on the remaining array members.”

No contest your honor, but there’s still that pesky URE probability during rebuilds, that can only be addressed by using triple mirroring in RAID10. So where short rebuild times and/or stable high performance are required (vs. higher reliability), RAID10 is a viable option.

[Vadim Carter] “as soon as there are three UREs within the same stripe – there is data corruption. I have seen it occur a few times.”

That’s pretty amazing (that you’ve seen it) given how low the chances of that are based on published URE rates.

Thanks again Vadim.