I'm bumping up against this as I configure a new machine by doing full-disk backup and restores. Frankly, I wasn't expecting great performance, since I'm dumping drives between a Mac Mini with a 5400 rpm drive and a hardware RAID FireWire 800 drive (Venus DS3R) with older IDE drives. But it still takes a while, and these numbers show things won't get much better any time soon on my low end :-)
dave
p.s. I'm considering replacing those Venus enclosures, which have given me good service except for a noisy fan, with either a Drobo (expensive!) or a 2 drive RAID Mirror enclosure (cheaper but more restrictive)
sfoskett
· 2 months ago
You're not alone, Dave! RAID rebuild on my Drobo takes about 8 hours with two 1.5 TB drives and one 1 TB drive. And slow interfaces and random access don't help - I'm only getting 25-35 MB/s on my Drobo and Iomega ix4, meaning it will take more like 12 hours to copy a single terabyte of data. Raw USB or FireWire enclosures might do somewhat better, but there's a massive risk of data loss with single-drive units, something I'll be writing about soon.
My advice is to buy a Drobo. It's not all that fast, and it is expensive, but it allows you to have a protected place to put your data that you can upgrade as time goes by. Need more space? Pop in another drive and let it do the work. No migration required.
deemery
· 2 months ago
One Drobo costs about 2 1/2 times OWC Raid Mirrored enclosures. A (presumably unlikely) hardware failure (e.g. power supply) on the Drobo would leave me hanging. I'm just not convinced the cost is worth it right now. The 'sweet spot' for me for a Drobo would be $200, and that doesn't look likely.
But thanks much for the Drobo notes, they helped me understand this a lot better than anything else I've read.
dave
p.s. just got Snow Leopard server and a 2nd Mac Mini. I already have Leopard server on another Mini, that serves as my 'inside server'. SL on the new Mini will replace the old G4/933 that's running Tiger server as my externally facing machine. I want to see if I can get IPNetRouter to work on SL on the Mini, that's a product I've had a lot of good experience with in the past, but it wasn't working quite right on the G4/Tiger Server for some reason.
johnmartinoz
· 1 month ago
I sometime have fun telling people that in effect, that disk drives are getting slower over time ... if you graph the IOPS/MB over those disk curves above you get a scary decending line. On a slightly different note, it's not just full backups that this affects. Remember in order to protect against "bit rot" most array vendors rely on performing regular RAID scrubs, these rarely happen at the maximum rate for the drive (flush time above) in order to prevent too great a performance impact.
As a result, it's unlikey that as disk drives get bigger that RAID scrubs will happen in a timely manner which will increasingly expose systems to a Media Error on Data Rebuild (MEDR) - i.e. if you do have to reconstruct your disk from parity, then one or more of your blocks wont read correctly and your RAID reconstruct fails. The affects any N+1 redundancy scheme including RAID-10. Unless you're using dual parity techniques, you'd better hope you've got good backups, which as disks get bigger, will also get harder and harder to do.
If you're interested in the math for this and how it affects reliability, check out "A Highly Accurate Method for Assessing Reliability of Redundant Arrays of Inexpensive Disks (RAID) by Jon G. Elerath and Michael Pecht in IEEE TRANSACTIONS ON COMPUTERS, VOL. 58, NO. 3, MARCH 2009 a copy of which can be found here http://media.netapp.com/documents/rp-0046.pdf"
All Comments
dave
p.s. I'm considering replacing those Venus enclosures, which have given me good service except for a noisy fan, with either a Drobo (expensive!) or a 2 drive RAID Mirror enclosure (cheaper but more restrictive)
My advice is to buy a Drobo. It's not all that fast, and it is expensive, but it allows you to have a protected place to put your data that you can upgrade as time goes by. Need more space? Pop in another drive and let it do the work. No migration required.
(presumably unlikely) hardware failure (e.g. power supply) on the Drobo
would leave me hanging. I'm just not convinced the cost is worth it
right now. The 'sweet spot' for me for a Drobo would be $200, and that
doesn't look likely.
But thanks much for the Drobo notes, they helped me understand this a
lot better than anything else I've read.
dave
p.s. just got Snow Leopard server and a 2nd Mac Mini. I already have
Leopard server on another Mini, that serves as my 'inside server'. SL
on the new Mini will replace the old G4/933 that's running Tiger server
as my externally facing machine. I want to see if I can get IPNetRouter
to work on SL on the Mini, that's a product I've had a lot of good
experience with in the past, but it wasn't working quite right on the
G4/Tiger Server for some reason.
As a result, it's unlikey that as disk drives get bigger that RAID scrubs will happen in a timely manner which will increasingly expose systems to a Media Error on Data Rebuild (MEDR) - i.e. if you do have to reconstruct your disk from parity, then one or more of your blocks wont read correctly and your RAID reconstruct fails. The affects any N+1 redundancy scheme including RAID-10. Unless you're using dual parity techniques, you'd better hope you've got good backups, which as disks get bigger, will also get harder and harder to do.
If you're interested in the math for this and how it affects reliability, check out "A Highly Accurate Method for Assessing Reliability of Redundant Arrays of Inexpensive Disks (RAID) by Jon G. Elerath and Michael Pecht in IEEE TRANSACTIONS ON COMPUTERS, VOL. 58, NO. 3, MARCH 2009 a copy of which can be found here http://media.netapp.com/documents/rp-0046.pdf"