4 ms·

RAID 6 with 32 drives. All the things you would not do while the array is rebuilding.

montecarl 8y ago
I aware of the issues one can have with rebuilding a large raid array. It seems like you will always hit some parity issue upon reconstruction. What is the proper approach here?
- wmf 8y ago
  Either declustered RAID for faster rebuilds or RAID 60 with smaller stripes.
nine_k 8y ago
Why, RAID6 can rebuild online, because it turns temporarily into a RAID5. Even RAID5 can be used while rebuilding, in read-only mode, because data from the remaining disks is sufficient (else rebuilding won't be possible).
- overcast 8y ago
  RAID5 can be used normally while rebuilding. Albeit at reduced performance. It's definitely NOT read only as that is effectively the same as offline in a production environment.
  - nine_k 8y ago
    Depends on your usage pattern. You might be hesitant to allow writes without redundancy, especially if you store something important which is mostly read-only anyway (e.g. 95% of operations are reads). For a large write-heavy setup + "we will restore from yesterday's backup" mode of operation, you may likely be better off with a RAID10 which is faster. (Though RAID50 and even RAID60 are a thing.)
    - overcast 8y ago
      Sure, but it's not offline, ever. The debate isn't about the best RAID level for your usage.
ChuckMcM 8y ago
I'm not sure I understand the comment. I've used dual parity RAID systems for over a decade now and they work superbly when rebuilding even during a drive failure. (aka in 'degraded' mode). I typically run them in 22 drive sets because that is how many drives fit on a single NetApp drive shelf.
- commentor10 8y ago
  With 32 drives you should have at least 3 failure tolerances. Might even want to plan some hot spares in there. The idea is to build a large file system that won't die and take your data with it - nor introduce downtime (with a suitable failure tolerance). And of course, have an offsite backup for actually backing up your data.
  - ChuckMcM 8y ago
    Agreed with the hot spare. Typical RAID reconstruction on these systems is limited to available I/O operations (IOPS) after accounting for the number needed to meet performance goals. If these are the only drives on a fairly beefy system you have lots of extra IOPS available so you should be able to reconstruct a drive in under a day if you wanted to. There are the usual caveats about age related failures happening in groups but at least anecdotally and from what I know from the folks who work in NetApp customer support usage across a much larger population, it is quite reliable.

I aware of the issues one can have with rebuilding a large raid array. It seems like you will always hit some parity issue upon reconstruction. What is the proper approach here?

wmf 8y ago
Either declustered RAID for faster rebuilds or RAID 60 with smaller stripes.

nine_k 8y ago

Why, RAID6 can rebuild online, because it turns temporarily into a RAID5. Even RAID5 can be used while rebuilding, in read-only mode, because data from the remaining disks is sufficient (else rebuilding won't be possible).

overcast 8y ago
RAID5 can be used normally while rebuilding. Albeit at reduced performance. It's definitely NOT read only as that is effectively the same as offline in a production environment.
- nine_k 8y ago
  Depends on your usage pattern. You might be hesitant to allow writes without redundancy, especially if you store something important which is mostly read-only anyway (e.g. 95% of operations are reads). For a large write-heavy setup + "we will restore from yesterday's backup" mode of operation, you may likely be better off with a RAID10 which is faster. (Though RAID50 and even RAID60 are a thing.)
  - overcast 8y ago
    Sure, but it's not offline, ever. The debate isn't about the best RAID level for your usage.

ChuckMcM 8y ago

I'm not sure I understand the comment. I've used dual parity RAID systems for over a decade now and they work superbly when rebuilding even during a drive failure. (aka in 'degraded' mode). I typically run them in 22 drive sets because that is how many drives fit on a single NetApp drive shelf.

commentor10 8y ago
With 32 drives you should have at least 3 failure tolerances. Might even want to plan some hot spares in there. The idea is to build a large file system that won't die and take your data with it - nor introduce downtime (with a suitable failure tolerance). And of course, have an offsite backup for actually backing up your data.
- ChuckMcM 8y ago
  Agreed with the hot spare. Typical RAID reconstruction on these systems is limited to available I/O operations (IOPS) after accounting for the number needed to meet performance goals. If these are the only drives on a fairly beefy system you have lots of extra IOPS available so you should be able to reconstruct a drive in under a day if you wanted to. There are the usual caveats about age related failures happening in groups but at least anecdotally and from what I know from the folks who work in NetApp customer support usage across a much larger population, it is quite reliable.