Scroll down for the video and also text tutorial. Hi Neil, I purchased your NetApp course and was amazed by how the material that you delivered was so easy to understand. I had been working with NetApp and had never seen the material presented the way you did it. I think you were meant to teach others and I can tell just by the way you present the material and how you include good hands on practice in your training. Throughout my career I have taken lots of professional classes that have cost thousands of dollars a class and I prefer your classes over all of those.
You have a special gift to take difficult subject matter and make it simple for others to understand. We're going to look at direct data access first. This is where clients hit a logical interface which is homed on the same controller that owns the aggregate. The system memory cache is a limited resource and we want to maximise its use.
The yellow data gets put into the top slot in our system memory cache on Controller 1, and the other data gets bumped down a slot. Again the purple data goes into the top slot in the system memory, and all the other data in the memory cache gets bumped down a slot. Acknowledgements are sent to clients as soon as the data is written into memory. This occurs before the data is written to disk and optimizes performance, because it's much quicker to write to memory than it is to write to disk.
As far as the client is concerned, the data is written to permanent storage, even though it hasn't actually been written to disk yet. System memory is DRAM dynamic memory, it does not survive a power failure.
If there was a power outage at this point when the data was still in memory but before it had been written to disk, we could have a problem because the contents of system memory are lost.
If data was only written to system memory this would cause an inconsistent state because as far as the client is concerned the data has been written to permanent storage, but we would now have lost it on the Controller. If we lose power before the data is written to disk, it can be recovered from NVRAM so we don't lose it. NVRAM will write the data back into system memory, and from there it will be written to disk in the next consistency point. Looking at our example again, let's say that Controller 1 fails due to a power outage.
At this point Controller 2 will take over ownership of Controller 1's aggregates through high availability, it will then copy the pending writes into system memory from NVRAM.
WAFL is optimized for writes. As you saw in the previous example it writes many operations to disk at once in a single sequential consistency point. This improves write performance because it doesn't do separate writes to disk and then send an acknowledgement for each individual client request. It doesn't have to write metadata to fixed locations like many other file systems do metadata is data about other data, for example date created and file size.
This reduces the number of disk seek operations and improves performance. Let's see how that works. Here we're looking at a disk that's being used by another file system which has got fixed locations on the disk for metadata.
Buffer cache hits Indicates the rate at which the WAFL buffer cache was successfully queried during the last measurement period. Buffer cache misses Indicates the rate at which an entry was not found in the the WAFL buffer cache upon a user query during the last measurement period.
Total number of buffers Indicates the total number of buffers in this storage system. Number Number of available buffers Indicates the number of available buffers in this storage system. Number A high value is desired for this measure.
Number Average message latency Indicates the average time taken for the execution of the WAFL messages during the last measurement period. Milliseconds Ideally, the value of this measure should be low. Failures allocating extent messages Indicates the total number of times the WAFL buffer failed to allocate the extent messages. Number Ideally, the value of this measure should be 0.
All rights reserved. Filter: All Files Submit Search. Test Period. How often should the test be executed. The host for which the test is to be configured. Specify the password that corresponds to the above-mentioned User. Confirm Password. Confirm the Password by retyping it here. Authentication Mechanism. Use SSL. API Port. Name cache hits. Name cache misses. Caching only system metadata : If the working set of the storage system is very large, such as a large e-mail server, you can cache only system metadata in WAFL extended cache memory by turning off both normal user data block caching and low-priority user data block caching.
Directory find hits. Directory find misses. Buffer hash hits. Buffer hash misses. Inode cache hits. Inode cache misses. Buffer cache hits. Buffer cache misses. Total number of buffers. Indicates the total number of buffers in this storage system. Number of available buffers. Indicates the number of available buffers in this storage system.
A high value is desired for this measure. Answer Low performance striping Typically an administrator would add additional disk space before the file system gets full. Over a period of time as files are deleted, the stripes will balance out. On a full file system, it is desirable to add multiple drives as opposed to a single drive to keep some striping. On the first sweep after a new disk drive has been added, the new disk drive will get more writes than the rest.
But the data is spread evenly to the disks precisely because so much more gets written to the new one on the first sweep. Because so much data is going to it, it will not stay empty for long. As new WAFL sweeps occur, the basic effect is for data to migrate until all the disk drives are equally full.
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