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Posts in Storage
Checking ext3 file system consistency on production systems
As an admin, there is nothing worse that the feeling you get when you determine you are dealing with file system corruption. Wether it's a lost inode or a corrupted superblock, I always get a big knot in my stomach when I figure out that corruption exists. With modern file systems like ZFS it's trivial to check the file system consistency while the server is online. But with older file systems (ext3, ext4, etc.) you typically needed to unmount the file system, run fsck and wait (sometimes for hours!) to throughly check the consistency of the file system…
$ read more →Using the ZFS scrub feature to verify the integrity of your storage
There have been a number of articles written over the past few years that talk about how silent data corruption can occur due to faulty hardware, solar flares as well as software defects. I've seen some oddities in the past that would probably fall into these categories, but without sufficient time to dig deep it's impossible to know for sure. With ZFS this is no longer the case. ZFS checksums every block of data that is written to disk, and compares this checksum when the data is read back into memory…
$ read more →Scanning for new LUNs on Linux servers
Storage management, the joys! Storage administration is one of those tasks that every admin does, and depending on your growth it may be something that consumes a lot of your time. If your servers are connected to a Fibre channel or iSCSI SAN, you probably need to periodically poke your systems to see new storage that is made available to them. There are several tools that can be used to do this…
$ read more →Measuring hard drive seek times
I've been fascinated with I/O and file system performance for years, and chose prefetch.net as my domain name after reading about pre-fetching algorithms in the book UNIX file systems (a great book that I need to read again). Since most applications access data that is not laid out sequentially on a hard drive platter, seek times come into play when you start to look at getting the most bang for your buck on random I/O workloads. This past week I saw this first hand. I was playing around with some disk drives and started to wonder how many seeks I could get per second…
$ read more →Thoughts on building your own NAS device
In a previous post I shared the research I did on the various NAS solutions that are available. I've been experimenting with the software solutions I described in that post, and have decided to forego a pre-built solution in favor of a DIY project. There were a couple of reasons for this: The hardware costs were significantly less than the pre built solutions. I have quite a bit more flexibility rolling my own box…
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