Vulnerabilities / Threats // Insider Threats
2/12/2013
11:48 AM
George Crump
George Crump
Commentary
50%
50%

3 Ways To Protect Cache Writes

Here's how to protect your storage from three situations that could cause it to lose data.

7 Cheap Cloud Storage Options
7 Cheap Cloud Storage Options
(click image for larger view and for slideshow)
Recently I discussed the importance of write caching in a VMware environment. A key issue when addressing write caching is protecting the cache until data is written to the hard disk.

Although protecting the data in the cache is always important, cache safety is especially important when caching writes. A write cache acknowledges the write before it is safely committed to hard disk. In write I/O-intensive environments, the cache always has data that has been acknowledged to the application but is not safely written to hard disk. If the cache storage area fails, this data could be lost and corruption might ensue.

The key three circumstances from which you should protect a write cache are: power failure, cache device failure and server failure.

[ Why run two backups, one for virtualized servers and one for non-virtualized, when one backup will do? Read The Virtualized Backup Gap. ]

1. Power Failure.

Power failure was a bigger concern when caches were mostly made out of server DRAM, but as I discussed in my article "The Need For Server Grade SSDs," most flash devices also use a small amount of DRAM to organize inbound data. If the device loses power, data in that DRAM area could be lost. The DRAM area in flash devices should leverage capacitors to charge DRAM long enough so that the data it stores can be flushed to the flash area of the device prior to the drive shutting down. There also has to be some intelligence in the drive to sense a power loss and take this corrective action.

2. Cache Device Failure.

Failure of the entire flash device can be a larger problem because many caches often are built using a single drive to keep down costs. A write-cached environment should provide greater redundancy. For server-side write caching, consider drive mirroring or PCIe card mirroring. Caches built from shared storage systems will leverage the mirroring or RAID built into the storage system.

3. Server Failure.

Server failure normally is not a caching problem, because the server hardware would typically be returned to operation and caching should pick up where it left off. In a virtual server environment, though, it is entirely possible to restart a virtual machine on another host if the primary host failed. If the caching was server side, the write data in the cache would need to be flushed somehow prior to the VM being restarted elsewhere.

To protect against uncommitted writes held captive in a failed server, you must get those writes outside of the host. This can be done by either mirroring the cache externally to a shared solid state device or by mirroring one server's cache to another server. Although both of these methods do introduce some latency because a network of some sort has to be traversed, they should still provide better write performance than hard disks, and reads would still be serviced from within the local physical host.

Flash storage has made it to a point of reliability that the technology is able to sustain the higher write traffic of write-back caching, and the surrounding technology has improved to make sure that the cache is protected in case of a device or server failure. With proper design, writes can be safely cached and both sides of the I/O equation can benefit from memory-based storage.

Our four business scenarios show how to improve disaster recovery, boost disk utilization and speed performance. Also in the new, all-digital Storage Virtualization Gets Real issue of InformationWeek SMB: While Intel remains the biggest manufacturer of chips in the world, the next few years will prove vexing for the company. (Free registration required.)

Comment  | 
Print  | 
More Insights
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
Flash Poll
Slideshows
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2015-4497
Published: 2015-08-29
Use-after-free vulnerability in the CanvasRenderingContext2D implementation in Mozilla Firefox before 40.0.3 and Firefox ESR 38.x before 38.2.1 allows remote attackers to execute arbitrary code by leveraging improper interaction between resize events and changes to Cascading Style Sheets (CSS) token...

CVE-2015-4498
Published: 2015-08-29
The add-on installation feature in Mozilla Firefox before 40.0.3 and Firefox ESR 38.x before 38.2.1 allows remote attackers to bypass an intended user-confirmation requirement by constructing a crafted data: URL and triggering navigation to an arbitrary http: or https: URL at a certain early point i...

CVE-2014-9651
Published: 2015-08-28
Buffer overflow in CHICKEN 4.9.0.x before 4.9.0.2, 4.9.x before 4.9.1, and before 5.0 allows attackers to have unspecified impact via a positive START argument to the "substring-index[-ci] procedures."

CVE-2015-1171
Published: 2015-08-28
Stack-based buffer overflow in GSM SIM Utility (aka SIM Card Editor) 6.6 allows remote attackers to execute arbitrary code via a long entry in a .sms file.

CVE-2015-2987
Published: 2015-08-28
Type74 ED before 4.0 misuses 128-bit ECB encryption for small files, which makes it easier for attackers to obtain plaintext data via differential cryptanalysis of a file with an original length smaller than 128 bits.

Dark Reading Radio
Archived Dark Reading Radio
Another Black Hat is in the books and Dark Reading was there. Join the editors as they share their top stories, biggest lessons, and best conversations from the premier security conference.