We’ve all been there: you have a certain Windows virtual machine with several disks of the same size and you don’t know which Windows-disk is in fact which storage LUN.
The VMware settings for this VM might look like this:
A while ago I talked about Hot Spares and how they are picked when a rebuild is necessary. It was almost 2 years ago and you can read it here.
Since then the rebuild / equalize technology has changed! Well, not for existing systems, but the new VNX family aka VNX2 does things a bit differently.
In the old days when a drive failed, a suitable Hot spare would kick in and the unprotected LUNs (regarding the failed drive) would be rebuild onto the Hot Spare. After a while, when the rebuild was done and the failed drive was replaced by a replacement drive, the data on the Hot spare would need to be copied to that new drive. This was called equalizing.
In the VNX2 (with MCx) this last step doesn’t exist anymore. So that means the Hot spare that was used to contain the rebuilt data is not longer a Hot Spare! It has become a regular drive! And that replacement drive will now be a new Hot Spare. When configuring a new VNX2 you’d see rules about Hot Spares and you simply don’t even need to configure Hot Spares anymore. Just make sure you have some unconfigured drives and you’re good. Your VNX2 will make sure they’re used as Hot Spares from then on.
If I remember correctly the DMX4 had a similar feature back in 2008, but it now flowed to the midrange platform as well.
If you have a primary LUN which is replicated using MirrorView/S and you decide to run SnapView snapshots on the remote side, consider that writes to the secondary LUN may have to wait for the COFW activity to complete before an acknowledgement is sent back to the primary array.
So if you’re performing tests on the remote site by using SnapView snapshots, you may want to consider suspending the MirrorView session(s) first in order to guarantee performance on the production site.
A good scenario would be to create clones from the temporary fractured mirrors and as soon as the clones are fully in sync, split the clone from its primary – being the MirrorView secondary – and start the resync in MirrorView.
After the write from the primary array (1) a COFW (Copy On First Write) (2) must take place if the write (1) overwrites a block that hasn’t been written to yet in order to maintain the point in time of the snapshot. After the COFW (2) is complete the acknowledgement (ACK) (3) can be sent back to the primary array.
So even if the snapshot isn’t used by a host, there’s already an increased activity on the remote array.
If the snapshot is in use by a host that writes to the snapshot, an unchanged block on the secondary LUN need to be copied to the RLP (Reserved LUN Pool) first before the overwrite can take place. This will also slow down any ACKs that need to be sent back to the primary array.
Be very careful when starting SnapView sessions on a secondary LUN and even more careful when using the secondary LUNs since it can have a severe impact on the response times of the primary LUN.
Most of the data we collect and store on our computers eventually ends up in some sort of archive. I think we can all agree on that, right? Do we ever throw anything away? Well, some data doesn’t really make sense after a while and can (and will) be deleted, but a lot of data “might be useful” after some time and so we keep it. And don’t forget the tons of digital memories we create using photo and video cameras! I estimate that I’m creating about 100 GB of digital photos and videos throughout the year and that’s increasing every year as well with the new cameras we’re using. More pixels, DSLR cameras, RAW photography and HD or even 4k HD videos are probably taking up most of the space we need extra each year.
Wednesday September 11 it was all over the news: all my popular news resources mentioned in one way or the other that Cisco is now into storage. The “Software Defined Data Center” buzz word is “buzzing” since the beginning of 2013, at least I didn’t hear much of it before that.
Many companies (including my employer Open Line Consultancy with Storage As A Service and Backup As A Service) already do business this way for years, it’s just that all of a sudden it has a popular name that everybody’s using since this year. But thinking about clouds with automated processes to fine tune and schedule every wish for storage, cpu or memory has really become popular. And with Cisco now acquiring Whiptail, this vendor will now be able to participate in this rising market space.
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