Raid 6 rebuild time 4tb?

Question

RAID

Hello.
Actually the essence of the problem.
There are many file shares on a bunch of different servers that have been configured for many years in turn by people with a strange attitude towards architecture in general.
File balls are in demand and need constant access to them by about 100 users at the same time during the working day.
And so there is a task to unite all this business on what that 1 disk shelf or something like that.
So, I counted about 27 TB of data and naturally everything grows gradually.
I'm not really an expert in Raid issues, I need advice on this.
For example, I will roll out a software RAID 6 of 11 disks + 1 for hot auto-replacement on a machine with 12 places.
All drives are 4 TB.
Everything is fine, everything works, but here 1 fails.
1) Approximately how long will the rebuild time of this disk take? 4 TB is not so small, and it must be borne in mind that no one will stop turning to the ball, especially if the disk crashes in the middle of the day.
2) I understand that at the time of the disk rebuild, that part of the data that was stored on it will not be available until the end of the rebuild?
3) What is the best way to design such a system of high availability of a large amount of data and ensure maximum availability?
4) How much is it right to choose Raid 6? it may be easier to stop at raid 5 then it will be easier to add disks.

Answer 1

1) count on a period of about a day. Even more so under heavy load.
2) misunderstand. In addition to the I / O performance drawdown, more rebuilds and a degraded array are no different from a healthy one to an outside observer.
3) it is important to understand that a raid is a redundancy of only one consumable - disks. From the cleaner, the electrician and other surprises, he will not help. Perhaps this is enough for you. Perhaps you need a clustered FS in general.
4) what is the difference between adding a disk to raid5 and adding it to raid6? raid6 for file storage is quite a good choice for such a number of disks.

Answer 2

1. Take the speed of the rebuild equal to the speed of reading from the screw and scale (~ 100MB / s).
2. everything will be available, but even RAID
3. from paranoia + the answer is higher
4. R5 is much slower (software) and much more falling apart
4.1. if you do it programmatically - maybe raidz-3?