In Columbia Pictures Indus. v. Fung, 2007 U.S. Dist. LEXIS 97576 (C.D. Cal. June 8, 2007), a file sharing case, the issue was the discoverability of Server Log Data (defined in the opinion as “the IP addresses of users who are downloading content items and who themselves seek the IP addresses of other users who have a desired content item”), which are transient data temporarily preserved on RAM (random access memory):

Defendants argue that the Server Log Data does not constitute electronically stored information and is not discoverable under Fed. R. Civ. P. 34(a) because such data has never been electronically stored on their websites or in any medium from which the data can be retrieved or examined, or fixed in any tangible form.... More specifically, defendants contend that since such data is transient and would require the installation of equipment for its storage, it cannot constitute electronically stored information.... Plaintiffs assert that such data is electronically stored information because it is being logged and written on the hard drives of defendants' servers where it is copied and stored.

First, as to the Currently Preserved Data, there is no question that such data is stored in a medium from which defendants can retrieve and examine it, and thus that it constitutes electronically stored information in defendants' possession, custody or control.

Second, as to the remaining Server Log Data, such data, at a minimum, passes through RAM and is written to temporary files on hard disks of the [defendant] Fung websites.... Although the parties have presented no authority which deals with whether data that passes through RAM and is written only to temporary files in transient space constitutes "electronically stored information" under Rule 34, defendants do rely upon a case in which the Ninth Circuit addressed whether data in RAM — a medium more transient than temporary files on a hard drive — is electronically stored information in another context.... In MAI Sys. Corp. v. Peak Computer Inc., 991 F.2d 511, 518-19 (9th Cir. 1993), the Ninth Circuit determined in the context of the Copyright Act, that software copied into RAM was "fixed" in a tangible medium and was sufficiently permanent or stable to permit it to be perceived, reproduced, or otherwise communicated for a period of more than transitory duration. It defined RAM as "a computer component in which data and computer programs can be temporarily recorded." ... RAM has elsewhere been described as providing "temporary storage." ...

Other courts have concluded that even deleted data on a hard drive which can be overwritten -- similar to the temporary files in issue here -- are discoverable under Rule 34, without addressing whether such data constitutes "electronically stored information." [Citations omitted.]***

In light of the Ninth Circuit's decision in MAI, and the similarity between the definitions of electronically stored information in the Advisory Committee Notes to Rule 34 and the Copyright Act, the latter of which was in issue in MAI, this court concludes that data in RAM constitutes electronically stored information under Rule 34. Since data in RAM is more transient in nature than data in temporary files on a hard drive in transient space, and in light of the authorities referenced above, the court likewise concludes that data in temporary files on hard disks constitutes electronically stored information under Rule 34. As the Server Log Data in issue is, at a minimum, temporarily stored on defendants' hard drives in transient space, the court finds that such data constitutes electronically stored information within defendants' possession, custody or control which is discoverable under Rule 34.