RAID and Data Backups

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Time
9 hours 49 minutes
Difficulty
Beginner
CEU/CPE
10
Video Transcription
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>> When it comes to providing redundancy for hard drives,
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the first thing you should think of is RAID,
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Redundant Array of Independent Devices,
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or you could hear Independent Disks.
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That's fine either way. The idea
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is there's redundant array.
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We have multiple disks acting as
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a single logical disk
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and it's usually for the purpose of redundancy.
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That being said, the very first RAID we look at,
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RAID 0 is not redundant.
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If I rule the world, I would call it AID.
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It's an array of independent disks,
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but it's not redundant.
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Without redundancy, what that
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means is if one of your disks fails,
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you've run the possibility of losing all your data.
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What RAID 0 does,
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is it takes two physical disks
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and uses a feature called disk striping.
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If there's 24 kilobytes
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worth of data to be written to the desk,
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12 kilobytes gets written to Disk 1,
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and simultaneously,
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the other 12 kilobytes is written to Disk 2.
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You get a simultaneous write,
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instead of a sequential write.
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It save time. It's a speed improvement.
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Not only is it faster for writing,
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but it's also faster for
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reading because its data is being
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located on Drive 1 or is being read on Drive 1.
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It's being located on Drive 2.
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You get a performance boost,
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but because of the fact that it's not
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redundant is not really a great choice for most servers.
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This would be good however,
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on media streaming servers,
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where we get that performance,
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but we don't really have the need for fault tolerance.
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If high availability is my need, RAID 1.
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What RAID 1 is, it's disk mirroring.
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I have two disks, each one in exact replica of the other.
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This provides really high availability
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because if there's a failure of one of the disks,
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it's very easy and very
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quick to transfer over to the other.
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You hardly ever need downtime at all.
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Drawback there is, is I'll
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always lose half of my disk space.
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By that, I mean, if I go out and buy
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two five terabyte drives,
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I have 10 terabytes of space.
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Five terabytes is for redundancy,
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so I don't get to use that per se.
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That's the one of the drawbacks to disk mirroring,
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but really good redundancy.
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RAID 5, disk striping with parity.
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This takes a minimum of three physical disks.
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I have disk striping,
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which gives me the speed improvement,
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but also on each disk contains parity for another disk.
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Ultimately, if Disk 1 fails,
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parity on Disk 2 can be
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used to rebuild the disk that's failed.
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That being said, this is
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a dicey process and sometimes rebuilding the disk
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can actually cause data loss or
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disk failure, is not ideal.
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RAID 6 is coming around to replace RAID 5.
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Here we need four physical disks.
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By using four physical disks,
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two disks are for fault tolerance,
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so not as many as two drives can fail.
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That's a little bit better of the redundancy.
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RAID 10 or sometimes referred to as 1+0.
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We said disk striping,
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the stripes that isn't fault-tolerant.
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What if I'm near that
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shapes that to another set of disks?
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That's what RAID 10 is. That requires
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four physical disks as well.
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Of course, halfway disks space would
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be used for fault tolerance.
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RAID is always discussed on the exam.
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Expect to get questions,
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expect to get a couple of performance-based questions.
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Thou shall know that I read.
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Another hot topic is going to be backups because
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even though we have RAID and please file corruption,
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malware can affect the entire RAID array.
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RAID doesn't really protect our data
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that way we need it to be protected,
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so we backup our data.
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There are multiple types of backups we can use.
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There is a full and incremental,
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a differential and a copy.
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The full is the easiest to understand
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because a full backup backs everything.
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Incremental backup backs up what's
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changed since the last backup of any kind.
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We do a full backup on Sunday night.
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We do an incremental on Monday,
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that back up cell was changed since Sunday.
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We do another increment on
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Tuesday and back up will change since Monday.
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An incremental Wednesday backs
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up which changes since Tuesday.
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This takes less time in backup.
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However, in the event that we need to restore,
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we have to restore the full backup
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in each phase incremental.
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That can take a little longer.
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A differential backup backs up
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which changed since the last full backup.
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We do a full backup on Sunday.
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Monday is incremental and
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backs up was changed since Tuesday.
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Tuesday's incremental, which changed since Sunday.
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Wednesday is incremental, which changed since Sunday.
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This is going to give us a quicker
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restore because we have to
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restore the full backup in the most recent differential.
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All of this has to do in
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Windows environments with a little bit
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called the Archive Bit.
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A Archive Bit is just a flag that pops up and says,
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"I've changed. I need to be backed up."
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When you do a full backup,
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all the bids get reset.
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That's just a way of acknowledging
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I've backed up everything.
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Everything that needs to be backed up is backed up.
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On Monday as files start to change,
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those flags pop up.
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We do an incremental Monday
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night and that backs up everything for
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the day and it clears the bits
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and the signals that's taken care of,
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Tuesday's new files are modified,
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the file pops back up.
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Tuesday's incremental backs up which
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changed on Tuesday and clears the bits.
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The differential backup is different from the other two
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because the differential bit
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backup does not clear the bit,
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which is exactly why Mondays files changed.
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It backs up everything has changed since
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Sunday. The Bit isn't cleared.
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As files pop up Tuesday,
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you have the things from Monday with
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flag set and you have the things from Tuesday.
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We backup everything since the last full backup.
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There's also a copy. With virtual machines,
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you can copy specific files
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or you could do a full backup.
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This just does not reset the Archive Bit.
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Also with virtualization, we now
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think about just reverting to Snapshots.
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Whatever our strategy is,
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we need to make sure that we have fault tolerance
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for our data as well as our hard drives.
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